How to know what is "fair"?

Fairly new to TRP, only really found out about this place 3 or 4 weeks ago, reading through sidebar books and slowly getting a grip on it. Signed up for the gym last week and started out on a PPL program this morning, starting to take better care of myself (I'm underweight rather than overweight though so trying to eat better & more). I've also started the hunt for a new job (current job is well paid, high status, just boring).

Wife's SMV has definitely declined since we got together, probably put on 10 pounds before our daughter came along and maybe another 20 since. She is working on losing weight but it's definitely slow progress.

Was fairly classic blue pill case, did everything for my wife and daughter, paid for everything, stopped going out with my friends all of the usual stuff. Been together 8 years, daughter is 4, married 2. In the last few months things had progressively got worse (my anger issues and her starting working regularly with lots of women on the CC). This has lead to her wanting to go out more and do more things with friends while I was staying at home with daughter. I got butthurt about this and we argued etc. things got better for a while then back to how they were, usual cycle. This culminated in her nearly meeting up with someone she works with and "going for a drive", she claims it was only for someone to talk to, I think we all know what that means. I found out before anything happened (she's a shit liar) and things have been slowly getting better, I'm still not trusting her but TRP is getting me to the point of understanding that I don't necessarily need to trust her as I know that if anything like that happens again it's over, and she is now well aware of that too.

What I am here for advice for really is trying to keep a healthy relationship in terms of what I deem as acceptable to me for her to do without compromising in what I am happy with, or should I even be worrying about that? For example this man she was going to meet from work if she has a work event (optional, meal out or something similar) that he is likely to be attending I do not want her attending, is it acceptable I say no? Should I give a fuck if he is attending? Objectively speaking his SMV is probably the same or slightly lower than mine. What about things like bachelorette party's for friends / colleagues? Should I care, let her do what she wants but ensure she arranges a babysitter and make myself busy that night as well?

EDIT: Follow up question, if I set out a boundary and she wants to step over that boundary, what are my other options/retorts than divorce?