am I overreacting?

my boyfriend is leaving to visit Syria next month. he just contacted an old ex, that he saw once. they were dating online, she lives in Syria but he didn't like what he saw when he got there. he said he wasn't interested in fatties. they went on a date and he gave her the cold shoulder ever since. but now that he's going to visit there, out of all people he decided to contact her. he sent the message right in front of me and I was like, really? he's like yeah, I told you I wasn't interested in her. then I'm like, so when you get there you're just gonna mess around with girls? he's like, I don't have anyone there... just family. and he's like... not like there's any other girls left. I got a little frustrated and went upstairs, he sent me a text message saying "You're acting like a child". am I over reacting?? I thought you're not supposed to contact old exes.