How would you react if your boyfriend did this?

my boyfriend works on the road a lot. we communicate throughout the day on our cellphones and through email. however, there is a website where our school clmates all communicate. sometimes I'll send a cute little message to him on there but one of his old female "friends" always has a little counter-comment to piss me off. Recently he has had such a hard time coming to my town, but at the school reunion in ANOTHER town a picture was taken with this same "female" leaning on my boyfriends back smiling into the camera...hmmmm....he says I'm over reacting...yea....right! what would you do?