I am more curious what people think of this idea of threatening physical violence when you find out your SO was cheating.
FWIW? I think these things....
1) It is not ok to break into other people's FB, or to threaten people.
2) The acting out? Not uncommon. I think most women are used to that possibility.... there's a reason why women get hurt/killed by partners so much. It is not ok, but it is there.
On his part? I think it may be part of that whole shock/denial stage that is in the first stages of grief. With some of the anger stage thrown in. And a lack of self control and/or experience with shocks. One could wait after the initial wave from emotional brain and try to avoid any behavior until rational brain gets a chance to kick in again. That's why some people "feel numb" at first. It protects them from hurting too bad at first.
IME, people who don't like to sit with yucky feelings are quick to "get them away" as fast as possible. It is sometimes easier to blame "the new person" than the cheating partner and think that new person "made them" do whatever. Because one is experiencing internal conflict. Still wanting to love/trust the cheater, but struggling with betrayal, so it's easier to "outsource" all the garbage feelings on "the bad stranger."
Rather than to sort through those feelings and look closer to home and ask why the cheating partner cheated/misled them, etc. Or how one may have contributed to the situation making (neglect, ignoring, always having a cow, etc)
3) I would walk away from her. Not even try to be platonic friends. Because she didn't clear that up first before dating you and you don't deserve to be treated that way. You don't need to be with a dishonest person. To me she would have messed up trust too much for me to trust again.
I didn't inquire much into their relationship and what agreements they had about seeing other/FWB when apart. I really didn't want to know (my bad).
4) I would change your vetting practices to ask rather than ignore in future. That behavior does not serve you well. The last thing you need is some jealous person with a gun. FB threats is bad enough.
But I believe women should be free to make their own choices.
I think everyone is free to make their own choices. But they are not free FROM the consequences of those choices.
On your end? You did not ask. So she didn't have to directly mislead you. I don't know if it was lies of omission or what... but in the end you became an unwitting cheating accomplice. She did not obtain your consent for that. You got used.
Your next behavior could be to dump the cheater completely and move on.
That she also misled him too and he's having a cow now? Well, you are out of the picture. Let her clean up her other behavior messes WITHOUT you in it.
Galagirl