Clearly when one is in a committed relationship they should not cheat. This happens to her a lot. Attractive young woman. My conclusion is that things are fine at first then her mental instability becomes clear and they try to end it.
I think she does not make it easy for them to end it, her manipulation tactics etc.
So i am not convinced the cheating on the guy's part comes first, I think she becomes scary, they need to end it. She refuses to end it. At the time of these confrontations with the "other women" My guess is its pretty over between her and the guy only not in her eyes
She stalks. Fatal attraction, she can't let go. Only one comes out of this alive and all that good stuff.
He has just proven she stalks, she pursues, she won't let go, she won't take NO for an answer long before she met Travis.