My boyfriends ex has been harassing him: How can I move past this?

Since we had a break back about almost eight months ago ( I’m now seven months pregnant ), he was seeing someone and finally came out to say that he was, and so was I, but he knew about me. But she has continued to harass him and constantly message him. So here we are, present-day, and he’s been getting calls about her house needing to get fixed cause his co-workers messed up. But then brings up about the two. And she does this late at night. He’s been trying to keep the peace cause, according to him and everyone else, she’s crazy and would get vengeance cause he chose me over her. Now he’s going to file a restraining order on her, and she messaged me the second she found out about that and told me all this stuff about how he loves her and doesn’t want to be with me and how they had sex a month and a half ago. ( we just moved into our home a month and a half ago.) How can I move on and choose to believe him over her? I keep hearing from other people who know her that she’s upset he chose me. I’m trying to just believe that she is crazy, but my insecurities get the best of me especially being pregnant.