My situation - I have a daughter age 6 from previous relationship, me and my SO are expecting a baby girl November 13th (his first)

So i receive a Facebook message from a boy telling me "please ask your boyfriend to stop messaging my girlfriend, his creepiness isn't appreciated as we have just had a baby ourselves, he should be focusing on you and your baby" my heart stopped! He also showed me a screen shot of a message he sent to my boyfriend asking him to stop messaging his girlfriend, which my boyfriend didn't reply to and certainly didn't tell me about. I searched for the boys girlfriend as well, she's obviously beautiful and blonde and thin (I'm very not) and the last picture she posted was of her with loads of makeup up and bra top on laying down with her new baby which of course, my boyfriend has "liked"

I'm yet to talk to my boyfriend about this I just wanted to gather some opinions first. He used to acuse me of cheating (even when pregnant) gets Jelous and always logs off Facebook on the computer so the next user can't see his profile even though mine is logged in 24/7.