Like others said, there is so much going on here. You have your personal issues, there are issues with the marriage (infidelity) and also situational/temporary issues. AND you're keeping all this inside and have been for a while. I have NO idea how you're feeling, BUT I know what it's like to keep everything inside. One day you're going to 1) explode over something trivial or 2) have a breakdown. Not a mental breakdown, but just a situation where you feel you can't do it anymore. You're definitely teetering on either one.
First, I suggest communicating with him and telling him EXACTLY how you feel about whatever you can verbalize. Sometimes it's hard to articulate to someone else exactly how you are feeling, but once you get going, it's like a waterfall. Sometimes, the other person doesn't know how you are feeling and your non-verbal communication could be signaling him to react a certain way. I definitely think you need to communicate as much as you feel you can say. Let it all go. There is no need for you to carry the entire burden by yourself.
Second, read "Emotional Resilience" by David Viscott. Someone on this board suggested it and I'm reading it right now and it's an EXCELLENT book. It talks about Emotional Debt and Toxic Nostalgia and so many other things that could be causing you to react the way you do and explain some of your passiveness. It's an excellent read even if you didn't have the marital issues.
Third, pray. Pray for guidance and understanding and the ability to make it through the day. It can help make the day bearable.
Fourth, take a mini-vacation away from him. Go to a place where he can't find you or contact you, unless it's an emergency. I mean, it could be somewhere local--a nice B'n'B or spa, or even somewhere that's a plane ride away. I'd actually really say that if you have friends/family further off, go stay with them for a weekend and just have FUN away from him.
This is just my
from reading what you've posted. I also think that the marriage can be salvaged, but you have to deal with your own issues to clearly see how to deal with the marital issues. (((((hugs)))))