More info is needed. 

Does your son live on his own?

How far away is he? 

Do you spend Friday afternoon - Sunday evening with him, or is it a quick lunch? 

Are you prioritizing your marriage in any way? 

Having a child with special needs is difficult. But I also think it's worth noting his level of independence/care needed since he is an adult. 

IMHO you have something entirely wrong. Your marriage and your mate are the only top priority. Kids, either minor or special needs, are the top responsibility. They are not the top priority.  Neurotypical/able bodied kidults are neither the priority nor are they a responsibiity.  I doubt that she is jealous, I would bet that she is not accepting of her marriage and her own quality of life not being THE priority for her DH.

Priority and responsibility are two very different things.   Your mate/marriage is the priority, your SNKID is a responsibility.

If you do not figure out how to set and invest in this reality, stop wasting this woman's time and end it.  If you cannot prioritize an adult relationship and a mate, don't vicitimize yet another partner.

I recognize that your kidult child is special needs.  However, you should not sacrifice a mate or a marriage on the alter of martyrdom to a special needs adult child.  Find a better way.

Good luck.

The truth is that most 23 year olds are living their own lives and not spending every other weekend with a parent. This is probably what your wife expected. This is the normal progression of adulthood and families. 

If your wife decided to invite her nephew/best friend/neighbor/college friend over EVERY other weekend - you would probably feel put out too. It IS an imposition to  have outsiders in your home, even if they are well behaved and polite. To be hosting on your weekends when you just want to relax can be exhausting. I hope that you do all the leg work associated with his visits - buying groceries, cooking, cleaning etc

Do you and your son do special trips and outings? Go out to dinner? Go to the movies? Do you equally plan special trips and outings with your wife? Do you treat her as a valued partner that you enjoy spending time with? Do you pull your weight with chores in the home? Is your son kind and polite and considerate in your home especially towards your wife? 

The good news here is that your wife wants to spend time with you. Thats great because she is the person that will be with you for the rest of your days. Your son should be dating, going out with friends, traveling exploring, taking up new hobbies building his own foundation for a great life - not haging out with his dad every other weekend.

Maybe you need to think of the end point. Where do you want your son to be in 5 years? 10 years? 20 years? Where do you want your marriage to be in 5/10/20 years? Both are going to take work. Perhaps your son will need extra support to get there than a neurotypical person but that doesn't mean that you should be sacrificing your marriage to achieve it. 

You've got your son through childhood and his early adulthood. Now it is time to cut the apron strings and help push him out of the nest in a way that is appropriate considering his abilities. 

That is not to say that you can't see him - just that if he lives 30 minutes away he probably doesn't need to stay overnight regularly - he could just come over for dinner or meet you to see a movie and go to home after. Think back to when you were his age...did you spend as much time with your parents? Or were you doing your own thing building a life for yourself?

The 23 year old is capable of living independently.  That more than likely is not the case and it is very hard to find suitable  independent living situations for adults.  The time OP spends with his son could be a much needed respite for the BM.  This is one weekend, or 1/10 of every 30 day month.  I wonder is this a new arrangement?  Was OP clear with his wife about his sons need's and time obligations before they married?  The chronological age of 23 doesn't magically absolve a parent of their obligations to a differently abled child.  I am the outlier here but I would be very uncomfortable with a spouse who was jealous of time spent with my adult child and the schedule cited does not seem extreme to me.  Perhaps counseling to reconcile perspectives is in order.

I'm not sure jealous is the correct word. Dad seems content with how things are. Autistic covers a wide range. Could it be the son is capable of more independence and that is what step mom is advocating? Is son severely disabled and Dad refuses to even consider the idea of a group home? There's not enough info in the original post to justify 'jealous'.

"The time we spend together is important to me. ... I try to include her in our activities but doesn't seem interested anymore."

Devoting every other weekend to the child is not healthy for the child or the marriage. I'm not surprised the step mom is not wanting to be included. You are planning things that interest your son. She's an after thought.

You (and BM) are not going to be around forever. Your child is 23. It's time to plan for what happens when you are no longer here. 

autistic.  And wasn't going to be going away with adulthood.   If two days a month is causing this much problems.  What is going to happen if something happens to BM.   I all for the SP,  But you have to know when your have a autistic SS  He not going away.  It's a life long commitment 

'Do you do things with DW on non SS weekends,  A weekend trip,to a fancy town, meal at a good restaurant. Concert,  Just some alone time,  town with a craft fair. Just to get our and do different things. 

I used to employ several special needs adults from a couple of group homes.  They were great employees.  Extremely dependable, hard workers, great attitudes.

 I worked with their home administrators so I understood how to utilize those employees to their best abilities and to protect them in my business environment.  My special needs employees were mostly in their early to mid 40s and older.  They had great lives. They had a community in their home, friends, activities, etc, they worked and made their own money, they engaged well with my other employees.  

I did have one who seemed to enjoy telling me every morning when he arrived at work that he was going to kill me.  We would banter, I would ask him to not do it today. He woudl agree, and get to work.  He had the mental and emotional maturity of a kid in their early to mid teens but he worked his butt off.  He was very sensitive about his chronological age and other than the daily death threat script, I had no issues at all with any of my special needs employees.

I would get invites for events at their home a few times a year. I went to every one.  

The parents of my SN employees were always very engaged, would join them for lunch at my business periodically, attend all of their group home events, etc...  They were active in their kids lives but also very commited to making sure that their SN kidult children had as full lives as they could.  Most of them had trusts established for the long term care of their SN kids.

I am a huge proponent of group homes for SN adults so they can have some independance, friendships, belong to a community, and get the professional care and oversight they may need.  And jobs. If they can work, they should. Their parents should make sure that the do work.

IMHO of course.

I went and read your other post as well.. and see that there are apparently issues from both sides. she has a son that has caused concerns for you as well.  Perhaps a bit of her frustration is that you want to exclude one of her kids.. while still wanting your son to be a regular visitor as an adult? (I get that the two kids are very different situations.. but that could be part of it).

One thing you did say in your last post was that your wife thought you needed to seek some help for your son.  You mentioned group home.. so I'm guessing the extent of your son's disabilities due to his autism are on the end of the spectrum where he would not be suited to living independently.   It may well be that she thinks your son would be better off if he were living a more independent life as an adult... even if that was a group home.. because that would be a normal progression for him.. and actually be a potentially more enriching life than shuttling between his parents.

I'm not sure what activities you are doing with your son.. so not sure if they are things your wife would or would not otherwise have an interest in.  You also would have to examine whether there are things about your son's behavior that might be stressful or difficult to deal with for her.. does he have meltdowns.. is he loud... do you have to be careful to act differently when with him?

And.. every other week.. I'm sure your EXW needs that respite from caring for him.. if he requires a lot of support.. but your wife may feel that at some point that childhood "visitation" stops.  That your son would be living his life.. and maybe you would see him every other week.. but not in a full time residential every other weekend sort of way.. you might meet him for lunch.. see him saturday afternoon.. and since he would be living with others.. he would be "busy" doing other things. and not be as reliant on his parents for companionship.

I don't know... since this isn't a "new" issue. I'm guessing it was something she may not have either fully thought through regarding your life together.. or maybe she thought you had given her a different impression of what it would look like.  

I do understand you want to spend time with your son.. but she may not be as inclined.. and to be honest.. that should be ok..   It's also probably something you and your exwife should be looking into.. what your son's adulthood is going to look like because he could be living a more full life if he were not kept in "child" position between you two.  Eventually.. one or both of you won't be here.. and it's better that he have his own adult life independent.. so that it isn't as difficult of a transition.. better to do it now.. while you are both available for support.  

I'm not saying that you dont see him any more.. but maybe it's more in a social way than in a caregiving way.. and that might feel less intrusive on her life?

Could you hire a repsite worker to come and take him out for an outing so you and your wife could have alone time? I am a stepmom to a 22 year old DS/ASD ss and in the same situation, no possibity of group home on the horizon. So a very strong urge to escape this exists in me, yet I don't want to leave the marriage. Please listen to me... hire a repsite worker to take your son out so you can have some time with her. Or what she will find herself possibly doing is leaving your house for periods of time - what I am planning to do - for a couple of hours, just for myself to get out of the house.. Sorry but this is my life too what your wife is going through. Jealousy, resentment...it doesn't start off that way..trust me...it took a long time...So I have my 22 year old stepson every other day and every other weekend...and I hit my limit and started registering for a respite worker, without any assistance from my husband. We have not interviewed anyone yet. It's given me a little bit of hope though. Also what you may find happening with your wife is that she may start hitting the bottle 

What do you  see life like in 5 years?  Is DS 29  an adult / autistic adult.  Still be spending weekends with you ?   Will DW Still be around. ?  Is DW seeing you being nice to BM your ex. Giving her help.  This has to end someday .   You can't be 90 and still picking up DS. 

I always looked forward to the day when SK left.  That I would get that relationship, no kids relationship that DW and her Ex  had befor kids.  That type where one can say. Let's go to McDonald, with out babysitters . Phone list.  Ect.  On Friday, saying pack a bag road trip tomorrow. 
Peopke don't sign on for a life time of visitation .  You have a basic choice to make, now / down the road. Wife or Son.  Can't have both 

So based on this and your other post it sounds like you and your wife are actually both doing the same thing in a different way. You say you're son will always come first. Your wife with her troubled son seems like she has the same idea, her son is her priority. It may seem more noble for you because your son has problems that are not his fault and hers is choosing to misbehave. It's also easier to blame her for her child's problems, "no consequences etc..." in the end end though the problem is essentially the same. You both prioritize a child over your mate. Then no surprise it leaves you each upset. We instinctively crave to be our mate's priority, their our person that we choose for the rest of our lives. No one wants to be in the backseat of their own life. This is a recipe for an unhappy unhealthy marriage. Your mate must be your priority in a marriage. Children, grown or not, special needs or not, are responsiblilies that you and your mate should handle together. This distinction does not mean that you love them less or they are not valued, you don't have to be a bad parent to be a good mate. But you do need to make your partner number one. Maybe that means taking a stand against bad behavior together, make a long term care plan together. When I say together I mostly mean together in that you're working as a team in supporting each other, acknowledging how the situation is affecting your partner emotionally and doing what you can to show you value them. For her that may mean setting boundaries with her son and finding appropriate ways to keep her relationship with him but not allowing him in your family home. She can be loving and respectful of you and your feelings without throwing away her kid. For you it may mean managing care for your son and making decisions about his future, spending time with your son while also making sure her emotional needs are met and she feels secure that you won't just upend your life together like she doesn't matter for your son. She may or may not take part in how you care for your son, depends on what works right for you as a couple, but she should support you at home as you handle your responsibility. If she feels more secure and heard in your relationship then she may be more interested in your son. Make each other your first priority, show love and respect, attack the problems not each other. Then dealing with responsibilities and challenges as a team will be easier even if the team decision is that one player sits it out for this session or that you go in together. 

With a special needs child had to have come to a understanding, about this child.  Normal, [like  normal... nothing from normal ]. Kids age out get married move into.  Soeciao needs had to been a discussion about this kid, and his future .  Living with / BM/YOU/ Independent living home.  Had to be a discussion..