I think what you fear is what many BS fear: when I set my boundary, I know he will cross it and I'll have to do what I said I would do (kick him out, leave him, file for D, whatever). In other words, you know what kind of boundary you are going to set but are panicked over him doing the wrong thing. You can't control what he does, but you are trying to. Why does it panic you to think of leaving someone who wrongs you? I can tell you, that is what a codependent feels about their relationship--panic.
It's easy to say, "I will not tolerate this," and people are not uncomfortable. It is a lack of firm action when our boundaries get crossed that is in my view a BS's most common contribution to a dysfunctional partnership. The WS doesn't do the work, and our contribution is to stay anyway.
You will only feel calm if you know you will be ok no matter what choices he makes regarding his completely disrespectful family and/or the OW. There are so many toxic people that you figure, "He is going to be disloyal. It's going to happen. There's too much that can go wrong. He's going to hurt me somehow." You can't change that he is going to do what he is going to do, that's true. You cannot control him or his family, so you need to work on feeling good about yourself and your life and your boundaries anyway. Remind yourself that you do not need him. You can want someone but you should not need them.
We make ourselves strong not by learning to numb ourselves to the hurts but by learning to love ourselves no matter what our friends and family members do. They are not us. We are us. We decide our value. We decide to be happy. We are not ruled by puppet masters; we detach from their foolishness and love ourselves no matter what.
Tell yourself that no matter what any of them do or say, you are an awesome person and your H is lucky to have you. How can you establish and keep that feeling throughout the day?
1. Ask him to hold your hand frequently, and definitely if OW is in the room. Have a signal (cough, tap him three times on the back) if he needs to grab your hand.
2. Ask him to stay with you, by your side, at all times. Have a phrase that indicates he is messing up. "Oh, there you are. I have such a headache," for example. That's his signal to stay with you.
3. Ask him for a time limit on the day. Point out the time ONCE if he is forgetting. "Wow, it's already 3 pm."
4. Ask him to walk away with you if anyone says this, that, or whatever offense. Scratch the inside of his hand as a sign if he forgets that you aren't tolerating that insulting crap.
5. Be clear about what you will do (leave) if he breaks any of these agreements. Do not compromise your comfort. Be strong for you.
6. Probably avoid saying you will file for D if x, y, z happen unless you are sure you would follow through. If you really would, then say it.
7. Review and practice your signals several times so that you are both clear.
This is a highly toxic environment for you. This family is not a friend of the M, and if he values you, he will appreciate the necessity of protecting you in this openly hostile situation. But you also need to work on separating your worth and happiness from his dumb choices. Fake it til you make it. Do not let these people get to you. Sticks and stones will break my bones, but names will never hurt me. They only hurt you if you let them, so never let them see you upset. Don't give them that satisfaction. Review your plan carefully and have your exit if he messes up. You can decide later on how badly he messed up (hopefully he doesn't) and if the R can be saved. I remember exiting a wedding once when I was young because my boyfriend broke our agreement and kept getting sucked in to some chick's flirting, so I left. I thought, "F this humiliation." But he left five minutes after me, so he ended up getting it once he saw that I was not messing around with my boundary. I felt better because he shut her down fast when I left. Your H may need some reminders, but your protective boundaries are your job to enforce in your M, not his. Just see what happens. But have a system of protections for you that you and your H have set up.
[This message edited by OwningItNow at 3:35 AM, June 18th (Tuesday)]