First of all, BB I admire your honesty in talking about this, especially after your prior posts on the relationship have always painted it so "rosy".
As for what she did, couple of red flags obviously. Hitting you was bad, but if it was a first time thing in 3 years, I wouldn't worry too much about it. Good self control as well in not striking back. Although I can promise you that if you had hit her, she probably would have called the cops and you would be in jail right now for the weekend. The stalking thing, another red flag, but to be honest, I almost blame you for this and you have probably done other similar things that finally led her to checking your phone, stalking, etc. I know you said she doesnt care what you do as long as you arent fvcking someone, but I think that's a bunch of BS. Hear me out.....
You have always talked about your relationship as being one of openness, doing a lot together, etc, but something seems off here. It seems as if there is a severe lack of communication going in the relationship, or you are purposely hiding stuff, and that is your fault. First, I find it odd that you havent told your fiancee your assistants name. I mean you guys live together, have a kid together, and she doesn't know the name of the woman helping you out everyday? And why doesn't your fiancee know that you are training this woman for 3 hours a day during the week? It would seem like such a casual and everyday type of thing to tell your fiancee that I for the life of me cant figure out why you were hiding that. And why not tell your fiancee the day you were meeting your assistant that you were meeting her at starbucks to train her? I don't get it. I pretty much tell my gf everything, what I do, where Ive been, what I did at work, etc. Its just part of being in a relationship and communication, even about the most mundane things, is important. I am just trying to picture myself having an assistant like you, (and btw I also work out of my home very close to you in Pasadena) and my gf NOT knowing the name of whomever the assistant is. Just wouldnt make sense to me.
So either you were hiding the fact that you hold some feelings for the assistant, which I doubt, or your communication with your fiancee sucks, or you were purposely not telling the fiancee about the woman just to make her jealous. I don't know. Something just seems off there. I am not in anyway shape or form condoning your fiancee and her actions, but in a way, I don't blame her from how you were acting.
Also, I don't think I would have had marathon sex with her. Kind of rewarding her bad behavior don't you think? While I blame you for not being more open about what you do all day, at the same time, she could ASK.