Should I be upset or ??

So my boyfriend has a girl manager and she talks to him outside of work like texting him and adding him in stuff on Facebook and saying jaaacob with faces at the end...i find it to be flirting I'm really bad at trusting I was with a guy for 2 years and left me for a girl he didn't even know so it's kinda hard for me but he says there just friends and what not but I'm really upset and he seems to think it doesn't matter because she is just a friend ...and I said what if I talked to other guys wouldn't you get upset but he says no but I'm deffintly not going to talk to other men because I'm not that away i stick by my mans side and idk what to do help ???😭 oh and he's 22 and I'm 19 if that might make a difference...