Is my boyfriend still thinking about his ex or just trauma dumping?

He 24M is my 24F first boyfriend, and we've been dating for 7 months and met almost a year ago. From the beginning he wanted to take his time because his previous relationship (which lasted like a month or two and ended a year before we met) was too fast and he ended up in a toxic relationship with an unstable girl 22F. Like, he's the first time a man has said his ex was crazy and she actually was, as his friends have told me about her and she was genuinely insane, she even assaulted one of them.

The problem is that he mentions her often, which is okay. I may not have other dating experiences but I understand that couples come clean about their past. What bothers me the most is that I will say something that has nothing to do with her and he will randomly bring her up. For instance, yesterday night i told him I was reading a book and he randomly brought her up saying she took him to a flea market where he bought a book. And 30 minutes ago I told him I want to sell some mangas online and he said his ex used to use that app to buy stuff all the time.

He barely talks about their relationship but when he does he tells me the most insane things and he blocked everywhere because he says he wants nothing to do with her. And yet, he keeps bringing her up in conversations that have nothing to do with her.

I really love him and he is a really sweet and caring partner and has never given me any reason to doubt him, but I think this behaviour is weird. Moreover, right now we are in a sort of long distance relationship because he will spend a month and a half in his hometown, which is at the other side of the country and very close to his ex's hometown. I fear he brings her up constantly because there's a part of him that misses her and now that they're relatively close he will go back to her? I know it doesn't make sense because he has been actively avoiding contact with her since before we met but I can't help but compare myself.

I know I should bring this up with him but first I need to know if I'm imagining things and how to do so. Thank you for reading if you did!