Steve
Steve being Steve was super friendly when he met your ex. Your ex wasn't that bad, you both broke up because you just felt that it would be better so Steve didn't have any reason to be rude, Steve was just glad that you were now with him.
Tony
Your ex was an asshole really. So Tony took it into his own hands to sort him out. Tony strolled straight up to him & just showed you off completely, making your ex super jealous. Before walking away Tony shouted "Sorry for the mean, awful, accurate things I said! Have a good one!" And shot him a sarcastic smirk.
Loki
Loki didn't like your ex being around you, in other words, he got jealous. So whenever your ex was around he'd just walk over to you & get in between you both, he would scoop you up in a hug & walk away without saying a word. Your ex hated Loki.
Bucky
Your ex & his friends thought it would be funny to pick on Bucky for having long hair, however when Bucky took off his jacket & showed them his metal arm & huge muscles, they soon shut up. Multiple apologies were said before Bucky went straight up to your ex & punched him square in the jaw.
Peter
Your ex was flash. Peter didn't really take any notice of him, neither did you. Everyday you'd hear the same "You would rather date Peter over me? Really y/n!" every single school day so you just began to ignore it.
Thor
Your ex was just some asgardian you had a little crush on a while ago, that was before you met Thor and became friends with Valkyrie & Loki. Whenever he'd try speak to you he'd flirt, all the time. Thor got sick of it one day though.
"If you flirt with my girl one more time I'm gonna literally blast you to pieces with my hammer so don't even think about it!" With that he grabbed your hand and stormed away, leaving your ex speechless.