Responses
Kinda late but what you're supposed to do ( since the whole divorce process takes a while ) is to declare to you partner that you want a divorce and separate. If while you're separated and getting the divorce finalized you start seeing other people, that's fine. However, he's dumping her because he was cheating on her and fell in love with the person he was cheating with. It was the infidelity that led to the separation and divorce. Not the other way around.
is it really cheating when you fall out of love with someone? maybe they were not meant to be in the first place, it didn't seem like he was an asshole, he wanted to help her with the situation. But tbh, what happened to her is honestly the scariest thing that can happen to someone in my opinion.