I NEED YOUR OPINIONS!!!!

Okay context to this blog, I have this ex (we broke up 3 months ago and only dated for 2 months) and recently he's been acting REALLY childish. We might have slept together during the winter break (after our breakup) but we agreed to stay friends after, but recently I saw him at college because we apparently have a mutual friend (he just met her and ive known her since HIGH SCHOOLLLL) and he was seating with her when I went to join her (she invited me BTW) the whole time it was low-key awkward since we havent seen each other since winter break yk but I THOUGHT we were chill right??? apparently not cause the whole time he was acting annoyed and later that day he full on BLOCKED ME EVERYWHEREEE like what? I thought we were good??? I legit don't know why he did that, but even my friend says it's childish. CAN ANYONE EXPLAIN WHY HED DO THAT???  and its obvious that im gonna see him again because he apparently have a crush on one of my friend's friend....(btw there's been a lot of drama about the breakup for no reason and im tired of it)

Am I the problem???