I caught my bf texting his ex…am i overreacting?

So my bf and his ex were together for about a year and a half … it was tumultuous to say the least..public humiliation, constant cheating, and on and off from his ex. So we all run in the same social circles and we have like games we all like to play with each other and stuff virtually, I wasn’t in this gaming groupchat.

But one of my friends sent me screenshots and it showed by bf and his ex catching up, talking about where they work now, catching up on life, laughing at messages etc. I was belligerently angry the moment I saw the messages. I confronted my bf and he said he doesn’t see why it’s a big deal, he has no feelings for his ex and it was a group setting. But the thing about my bfs ex is that the ex always goes out their way to make conversation with my boyfriend.

I’ve previously told my boyfriend that him replying to his ex even if it’s just a hi makes me uncomfortable several times. He says he doesn’t care enough about his ex to ignore them it’s not that deep to him. My boyfriend completely removed himself from the group chats, even though I told him I still want him to have fun and play games just don’t reply to his ex. He told me he just doesn’t care to ignore his ex. and he says i’m overly insecure, but the thing is when our relationship started he broke up with ME because he wasn’t fully over his ex so of course I have some self doubt but he says I should be over it by now just as he is. I think I’m going to just drop the whole relationship