AITA for thinking my ex is crazy for getting back with his ex?

soo my daughters dad(30 years old) was dating this chick(30 years old) for like 8 months they moved to Florida together and they broke up like last month. In the 8 months they were together this girl was involved in everything when it came to our daughter and had to be involved in stuff when me and my daughters dad had to talk about our daughter. She always had to be there when he FaceTimed our daughter or when he and I were just talking about our daughters well being. I always had to be on speaker and all that. The girl wanted to even be in the group chat we have with his sister and his mom. I knew when he was texting me and when she was texting me from his phone. the girl disrespected me and got nasty with me when him and I were talking about our daughter. She accused him of cheating and then he kicked her to the curb. So then today one of me and his mutual friends told me that he and the girl got back together. He didn’t tell me so I texted him and I was like is there like something you need to tell me about the crazy girl? and he goes oh yeah we got back together she apologized. I was like over my damn dead body is this girl gonna be around my kid ! No questions no if ands or buts don’t care don’t wanna hear it.. and he goes I know she has issues but I wanna give her a second chance . I’m like she showed her true colors in the 8 months you two were together. He goes I know I won’t risk anything or won’t let anybody risk me from seeing our daughter so I know what I need to do. I’m just like why would you even put yourself through that again? he was so down in the dumps when they were together. He was so depressed. just why do men put themselves through that? I think he just will be with anyone so he’s not lonely.