Changed after sex?

This guy and I had sex and after it seems like he lost complete interest in me. I don’t mind being rejected, but this time is different because I don’t get it. He was basically prying after me all summer, would always flirt/hmu/etc. the sex was good, I made him c*m 4 times and we talked a lot in between.

He will literally flirt with my friends or other girls right in front of me and I just feel like he’s doing it on purpose- it makes me feel really used and also confused…

One of his bestfriends killed himself a few months ago so that’s the only thing that would make sense to me? I know he’s going through a hard time, so do you think this is just him acting out?

Or maybe he’s just an asshole and I sympathize too much. Opinions?