AITA for being upset my partner wants to be friends with my ex?

So I (14M) am currently in a relationship who we'll call Tyler (also 14M) we've been dating almost a month now which his relationships usually don't go past a week, he's known for being a hoe but he's asked me out many times throughout our friendship and eventually I decided to try it. Anyways he got my ex's phone number a few weeks ago to prank call them and now asked me if it's okay if he keeps my ex's number. Now I usually wouldn't care who Tyler's friends with but the ex in question is one that was very on and off with me usually using me as a back up and would cheat on me very frequently while I still stayed with them. Can I also add this ex is currently 17 and when we originally started dating I was 12 while they where 15 which is kinda weird, our relationship had gone on for a little over a year until they were fully bored of me and I finally lost feelings for them. I had told my boyfriend Tyler that I don't care if he's friends with my ex but I honestly do but don't want to sound controlling or anything. What should I do? AITAH?