Am I wrong for being upset with my kids’ uncle?

My baby daddy and I just broke off our engagement because when I was 39 weeks pregnant with our now 3 week old, we had a fight, he left, and was talking to other girls. When he had left, I called his brother and told him I was worried he would leave for good. He told me that he would talk to him for me and figure out what was going on. I found out that he told his brother that he cheated and his brother covered for him, saying he wasn’t talking to anyone. In hurt feelings after the breakup, I called him out and at first he claimed he had no idea. So I sent proof and he started saying how he’s “not part of it” and it’s “not his business” and how “he’s not his brother’s keeper”. But I feel like he can’t say that because he included himself when he could’ve said “I don’t want to be part of this” when I talked to him.