You can get all of the good stuff from a responsible roommate, dog sitter and handyman. 
 

like there is a lot of good in your marriage. You didn't mention anything about how your DH treats you other than things he does, which others could do. Is there any respect between you? Trust? I was going to tell you to disengage with your SS and stand up for yourself with your DH with regard to insisting on keeping plans regardless of SS not wanting to go etc. That was until you said your DH had cheated. 

That's a dealbreaker for me, even without the other issues going on in your life. Why woud you trust him to look after you if you were sick or dying when you can't trust him to be faithful?

You deserve better than staying with a cheating man who lets his kid treat you badly. 

I encourage you to get a roommate. Preferably one that can do stuff around the house and likes to walk dogs. Then you would have really improved your situation. You get all the upsides and non of the downside. 

Life is too short to put up with this nonsense!

Nothing in the "good" column pertains to your husband, specifically. So, all of that (and more) can be found elsewhere.

The bad column, though? I would have been out of there a LONG time ago.

Oh, the bad outweighs the good, for sure.  All of those "good" things can be obtained elsewhere, without the aggravation of a bratty, disrespectful kid or a cheating husband.  Move on.

How old is SS?  Whether or not he will be out of the house soon might count towards what you do.

Having said that, your DH cheating would have sealed the deal for me.  Sorry, but once a cheat, always a cheat. 

If your good and bad points are an honest effort...

Forget the bad for a minute.  The only positives you can list in your marriage are the same qualities you can obtain by hiring a service. 

Is that the narrative you want for the story of your life?

You deserve better, even if you don't know what better looks like.

If that is all of the good.....  you are getting the short end of this stick.  A Church can provide  everything on that short list.

Doesn't seem like you have much of a marriage and it appears that what you do need is a home health aide should you require health assistance should you ever become sick. I think the caretaking is why you tolerate your H's sh!t and you can get that taken cared of by having an aide via your insurance.

Also remember that stress tends to bring out dis-ease/sickness and dealing with all this chaos can be a cause to have your illnesses resurface~just food for thought.

Wishing you healthy vibes!

Good start.

NOW make a list of things that you need to be happy.

Priority in your own marriage would be one thing to include on that list. (If you and DH decide on restaurant A and SS wants Restaurant B, you go to Restaurant A, end of discussion. If DH can't even do that much for you, then you really don't have much of a partner.)

Once you make that list, then it's time for a convo with DH because you cannot continue to live in misery. If he won't hear that you're unhappy and if he won't make changes so that you will become happier, then your choice is becomes more clear. To be clear, HE is not responsible for your happiness--you are. But you can't be happy living in the current environment, so you need to take steps to change it.