Angry Hateful BD

My baby daddy chose being with someone else over giving our family another chance. Before her, we were always together, slept same bed, sex, trips, ect, we weren’t perfect but we had a very good relationship. (Not the point, just some background) He has now been with this girl for almost two years and has completely changed. He is now angry and hateful, blaming me for our child’s actions, he won’t listen to talk, he hangs up and ignores calls when i try to talk things out. His girlfriend does not like me, i have done nothing, haven’t even talked to her. She is very bothered by me. I want to almost blame his new demeanor on her but obviously idk. A lot of the times when she is around he is a piece of shit to me, and when she’s not around he is nice and flirting and joking. (Again not the point) What I’m not understanding is, why he has become this, he chose this, yes has lost his friends, me and his child. But why is it being taken out on me????