Did I overreact?!

So this girl (who I will say has always taken intrest  in my bf for example writing in his yearbook how nice is ass is, texting him, wanting to hang out at theme parks together, etc.) messaged my bf on Facebook asking a question that pertained to his penis. Of course I flipped out, but not just because of that but because my boyfriend kind of took her side saying "so what, are you going to fight her? What's that going to accomplish? What wiill that do? Just forget about it". He answered her question and then was like "why are you asking" and she's like "just wondering." I then asked him how he would be if the tables were turned he he said "Well that's different". Um not to me? If anything I think it's worse because it's not unusual for a guy to perv out on a girl, but I hardly ever hear of a girl being so blunt. And she KNOWS we are dating by the way. 
I trust my boyfriend 100%, and he would never cheat on me but still. Girls are sneaky. 
Now please tell me if I overreacted or if my reaction is reasonable. Because I still get mad don't thinking about it.