Is a joke with your significant other about how u find a random person in public approachable disrespectful?

My girl and I have mutual friends. I was looking through one of our friends' pictures on a social network and saw a pic of him with a pretty girl. Since he and I both are serious about our girlfriends, I commented on the pic saying what both of us would have been thinking,"I swear, if I wasn't damn near married..."

My girl saw this, started crying hysterically and immediately wanted to break up with me. However, she's made the same kind of comments jokingly, but about models and actors, but she says that it's different since the girl was some person that I would actually have a chance at approaching. Am I in the wrong?