The other woman

So I've been with this guy for 6 years. I call him my boyfriend but we are just really good friends with benefits. At the start of our relationship he was married but seperated. And she was with someone else too so it was all fine. Then he got divorced (she eventually wanted to remarry someone else) I had to go away for awhile for work and he got someone pregnant and married her so she can have health ins. But she wanted to be a family so he was basically like whatever. But once I came back to town we still hooked up and hung out. Well she found out about me and flipped. I get she was angry. But I don't understand why women flip on the other woman. Me & her didn't have a friendship, I didn't know her, we never met, I didn't say any vows to her. There's no secret woman sisterhood. There's no reason to be mad at me because YOUR man broke your trust and vows or whatever. That's between you and him. Instead of flipping on me and wasting your time go fix your relationship. I didn't force him to cheat, he was going to do it regardless who it was with. Stop blaming the other woman like men can't control themselves.