You don't.  She is just a girlfriend and has absolutely no say in the aggreement between you and jerkface.  I really doubt a judge would give it to him anyways.  

Just put your foot down with the ex and there will be no more conversation about it until she is older.  

My bet is that girlfriend wants to play happy family and show her off and be MOTY.   Much like a single guy uses little kids to snag a date.  

You have all the power right now.  Don't let them scare you  

Unless you are breastfeeding then I don’t see why you can’t let the child go every other weekend with it’s 9yr sibling. My DH and BM split when SS was only 6 months old. At 6 months old he was on a 4 on, 4 off schedule and he was absolutely fine. Then went to a 5-2 (dh primary).  That thing you tell yourself that YOUR baby absolutely needs YOU to sleep and get through the night is a lie. What’s the difference between a 7 week old spending 10-12hours straight in a daycare all day while mom works? You’ll say “well I get to pick her up and drop her off everyday.” ....True and you can do one on and one off with the kid and get the same result plus a free babysitter. The girl isn’t being immature, maybe premature because who’s to say she’s permanent at all, but she’s right about the sharing part. 

The Sunday afternoon visitation. Is the visit restricted to having to be in your home? 

Or is the father allowed to come pick up baby and , for example take baby home for a few hours or over to his mother's house to visit grandma?  And is the place of visitation (your home ,if it is) actually in the court order or just something you are more comfortable with and insist on? 

You do not nor ever shall be required to co-parent with your ex husband's partner. Even if they marry and have a dozen kids. There are two parents to your 9yr old and the baby. That's your ex and you. All communication needs to be between the actual parents. All court orders are between the two actual parents. 

It is your ex's choice to take visitation or not. He either takes what is in the order or he waives the visit. You are under no obligation to make different agreements on the side. Being the divorce ink is barely dry, I seriously doubt your ex has any room to run back and try to have anything modified at this early point. 

Do not agree to anything currently not in the order and/or parenting plan. 

The GF can whine all she pleases. She's not your problem nor is she your's to have to deal with. 

Is your ex taking the older child for the ordered allowed visitations?

I imagine this is very hard to deal with, him leaving you and taking up with the affair partner. And having to deal with her influence. But read on these boards about how damaged kids are when one bio parent makes it hard for them to love the other one, or to care for the new partner in a parent's life.

  I too don't understand why he can't take the baby for a few hours, even overnight.  He is her parent as well. And plenty of people leave young babies with their grandmothers for a night or longer. Or in daycare for an entire day, with strangers.

I would say Daddy is a valid parent, too. You don't own the baby, you don't have the right to be your children's gatekeeper. 

On the other hand, if he cared even half a sh!t about his brand new baby, he would have manned up and kept his pants on while you were pregnant. Babies are tender and precious and helpless, how can you trust a woman who helped break up your marriage to properly care for your breakable, non-verbal infant?

The only thing that worries me about your schedule is that the 9 year old will:

A. Get confused when you all play happy family every other sunday.

and

B.Start to resent that baby gets to stay with you but he has to go endure being marginalized at his dad's house.

Is it possible that you and your ex can work out that he takes the baby to his mom's or dad's or auntie's house alone so there is someone there who is a little more experienced in child care that has a vested interest in baby's welfare? Honestly, new GF really doesnt need to be involved in these EOWEs, the kids are there to spend time with Dad, not hang out with him while he's in the honeymoon period with his new fling.

and has equal rights including the right to take the child out of your home. 11 weeks isn't too young to leave for the day and go to dad's house and arguably isn't too young for overnights either. He should establish a custody order now and request at least all dat Saturday and all day Sunday visits outside of the home. As it is he isn't getting enough time with her and they are unable to form a bond. 

And why 22 months for overnights? What a random number. 

maybe from the stepmoms point of view: he told me It was over/getting divorced.  

we are going to be a family/have more kids and I am going to love and treat all of my husbands kids well. 

no need to have visitation with the kids mom there unless she is going to be nice to all of us.  

our future will include lots of family photos, birthdays, dinners, teethbrushings as a family and you will not be present, but your kids will.  you might as well start being nice and teach your kids this is the new normal and send them off with happy thoughts.  

don't teach your kids to be bad, just because you are bitter, they will not have a quality life.  

to him having an affair. I was in a unique position in that I had a crap ton of evidence of wrong doing and I made a deal with him. I said I would walk with him having to pay me nothing at all if he didn't make the other woman my children's stepmother. She is truely vile and a crazy person who is currently in a mental hospital and he took the deal. He married a lovely lady he met off the internet and the baby I was pregnant with is now 9. We coparent very successfully but I know a big part of that is because he isn't with the crazy bipolar nutjob affair partner. I would just about die if that woman had any influence in my children. Her own children were removed from her custody. So I feel you. I do. I was lucky he wasn't in love with her disgusted self . It's a truely horrific shit sandwich to eat when the affair partner wants to raise and influence  your baby.

My BFF's ex cheated on her when their son was just a year old. He married the affair partner. I have SO MUCH respect for my friend, who was able to love her son more than she hated her ex. She coparents like a boss with the new wife as they both now realize how worthless he is in the parenting department.

My friend doesn't blame the new wife. Who knows what pack of lies Cheater McCheaterson told her. She blames the sleezebag who broke his vows and will highly likely break them with the current wife, too, if he hasn't already. Their son is 7 now and he's a happy, healthy, awesome kid who loves both of his parents, his SM and the little sister she and his dad gave him. 

See, my friend's dad ALSO cheated on her mom and married his side piece. My friend knew exactly what is was like being a kid and having all of this adult shit dropped on her shoulders because her mom couldn't keep her anger and bitterness in check. My BFF's younger sister is 35 and still totally screwed up. 

Love your kids more than you hate their father. You have so much power in this situation and the choices you make in how to proceed will very likely permanently affect your kids.

You have control.  Do not cave to the demands of the X’s GF.

First of all you don't have to co-parent with her, she is just the gf and has zero say in your custody arrangement.  She's visiting him from the Philipines and he's about to be deployed to Afghanastan. Well, who knows if their relationship will last or if he'll bring home a new girlfriend from each country he goes to.  Personally I wouldn't even talk to her but deal with the other parent only.  ExH used to have his fiance then 2nd wife set up all visitation with me and now he's trying to do the same thing with wife #3 who barely speaks English.  It's annoying and entertaining at the same time.  

As soon as he's deployed I'd pack everything up and move back to Germany where your family and support is. No reason to stay in Texas. Consult a lawyer on this of course.  

Wait until he's deployed and pack up. He's going to have gf after gf around your kids. They'll have stability with you and your family. And sorry OP, but he's been cheating on you the entire time. You caught him this time because this one became serious and went about stalking you. 

Sometimes the partners we accept or even choose turn out to not be who we thought they were. That this POS is as F-d up as he is is good enough reason to minimize the exposure that  your children (though  his children also) have with him.  When you throw in the cheat partner... these kids shouldn't have to have any exposure to either one of them when the cheat partner is present.

The good news is that the problem goes away for 22-mos during his deployment.  Cheat partner gets ZERO exposure to either of your children during that time.  You will have plenty of time to get all of your legal, custody, and visitation ducks in a row while he is gone and be ready to address them from a much more confident place upon his return.

It is likely that he will return with another SO that he will dredge up while on deployment anyway.  So, start boxing in this toxic XH and get the structure in place to protect your children as much as possible.

This is such a toxic situation that even a 9yo can see it. 

Take care of  you and your children. Never tolerate toxicity in their lives introduced by the XH. He is their father and should be protecting them and not servicing his nether regions with a toxic manipulative presence that is not healthy for his kids.   No kid deserves that.

While I am rarely one to recommend that an X or kid be tolerated to interfere in anyone's current relationship, there are some sitautions that require boundaries and consequences for a parent who introduces toxicity to their own children.  This seems to fit that scenario.

All IMHO of course.

I worked with kids and families for many years. There is simply no excuse to do this to his own family. I don't know if OP dumped him right away once she found out, but he should have immediately dumped that woman. At least tried to behave like a decent father. And been there for his wife. This guy hasn't been around a whole lot for any of his kids because of his job. Dont' know why he fathered 3 if he's always out of the country, but that's another topic. I was fortunate because I met my current DH and has been a good father.  Yes the problem will mostly be gone, that's a big PLUS. OP there are better men and fathers out there. Time for you to count him out of your life altogether. Don't think he's been there much, and I do beieve he's cheated on OP for many years.

If you aren't bitter you're just amazing and so well-adjusted it's disgusting!  I am the victim of a cheater as well.

He can't possibly expect you to be warm and fuzzy about his mistress wanting to play mommy!  That's just unrealistic!

I have to agree with a previous poster...It's time for you and their father to have a very adult conversation and you tell him how you feel.  Give him an out if he seems like that is a good idea.  Move back to Germany...get your life back!  Plenty of women raise children on their own too.

I raised my son on my own...Best decision ever!  I told dear old dad he didn't have to a pay a dime if he just went away, and away he went!  Ironically, he was a Marine that came home on leave and married a friend of mine without me knowing.  Our son was a month old and I was under the impression WE were getting married!  Imagine my surprise!  LOL