Jealousy Sucks

Ok so I don't really care if I'm agreed with or not but I need to voice my opinion on this... Me and my gf have been dating for some time now and have gotten really close together. She is very beautiful and can sometimes be naive on how guys are. One day this guy texts her who she dated a while back. She asks me "can we be friends" and even though I was a little weary I said sure. Later on I found out that he was texting things like good morning gorgeous, and hey hun and it ticked me off. She says it was just friendly gestures but I know how guys are. You don't say crap like that to another guys girl and I told her how much i hated that... She thinks that i am being jealous but Im just trying to be protective over her even though I know she would never hurt me...