I need advice!

Can someone please help? My bf and I have been dating for a while and all of the sudden this girl I used to be friends messaged him. Tells him he’s cute and stuff and ends with saying I’m going to ruin your relationship. My bf ends up blocking her and tells me the story but I’m still weary because I saw another message that said “I wasn’t going to tell her I just thought it was mean that you blocked me after a nice conversation blah blah blah” and that got me concerned. I trust him but it bothers me that I don’t know the full conversation because at first he said he never answered but later said they talked for ten minutes. So what??? And this chick has a boyfriend so even worse. I just don’t know how to react. Every time I ask him he gets upset and won’t tell me so that doesn’t help. I don’t know if he could have asked for nudes or something(she live 1.5 hours away). I’m sure you guys know how I’m feeling I just need help!