I voiced my concern and was met with, "well if you don't like it, you can leave . . ."
Since you stayed instead of leaving when he gave you this stupid ultimatum, you showed him a bunch of things, namely:
1. That you are desperate to keep him;
2. That he means more to you than you mean to yourself;
3. That he is the most important person in the relationship;
4. That he can continue to dupe you and see his lover as often as he can make the trip and use her sister and family as decoy;
5. That he can continue to snow you by pretending he doesn't understand what you say.
He did all those things because you allowed him. You essentially told him he could because people will try to get away with doing whatever they can get away with doing.
I am really struggling with this because I feel that he will make the family issue the main argument- accusing me of telling him he can't hang out with his family
Of course he will. He uses everything you say against you. He uses all of your insecurities against you.
and I fear it may be a deal-breaker for him.
That's why you're still there putting up with his bullcrap and all this silly drama. He keep letting him know you love him more than you love yourself.
Is it unrealistic of me to expect him to set boundaries in this situation because of the close relationship she has with his own family member? - I think that he doesn't want to set boundaries or change anything because he is still trying to hold on to their connection through her sister. (I did my best to explain the situation)
Do you know how often people come to internet boards like this wanting their spouse to change, while they, themselves, don't want to do any changing? It's every day. It's all the time. And you have joined their ranks.
It's also very common for people throw the word "boundaries" around when it applies to their spouse/partner, but they really have no idea what that word means.
So I'm asking why you want HIM to establish and enforce boundaries, but you don't have any boundaries yourself?
Boundaries are the personal values and rules of conduct that a person places on THEMSELVES and those in their life. That means you can only establish boundaries for yourself. You cannot require someone else has boundaries because, again, boundaries are borne of a person's OWN value system and are up to each individual to establish for themselves. Either he has boundaries or he doesn't. Whether he has any is not for you to be concerned with. You can only concern yourself with your own boundaries.
So if you want anyone to have boundaries, you have to have some. But you don't. You just keep letting this man run over you as he pleases. If there are things he does that you don't like and he is disrespectful to you, which there clearly are and he clearly is, then you have to establish your own boundaries and determine you don't like those disrespectful things he does. And then, you have to decide what to do about his disrespect.
You cannot decide to keep telling him and keep arguing with him because all you're doing is arguing. And all he's doing is pretending he doesn't understand what you say. Having boundaries is not about arguing a person into compliance because you can't MAKE anyone do what you want. You can only show them that you won't tolerate what they do and won't tolerate them disrespecting you, and you can't keep telling them over and over "I'm not going to tolerate this." You have to show them that you're not....by leaving since they refuse to respect your boundaries.
Until you have respect for yourself and establish your own boundaries, your husband is going to keep on disrespecting you because you don't respect yourself. Since you love him more than you love yourself, you might as well stop arguing and stop trying to explain things to him just so he can keep pretending not to understand and using everything against you.
And just for the record, they have done much more than kiss. "It was just a kiss" was just another snow job that you fell for.