omg i have a song for this...
[ame="http://www.youtube.com/watch?v=Ct2LUz5Fhsc"]YouTube - Cars - My best friends girl 1978[/ame]
well, i don't think it's that big of a deal. his ego was injured when his girlfriend left him for his friend or whatever. and then to add to it he has to see her all the time. it's like waving a nice piece of steak in a dogs face.
but i think that he would be the stupidest man alive to actually entertain ideas of being with her over you. he probably wants to hurt her the way she hurt him. you never left him for his friend and you've been very loyal and generous to him.
if he is a good guy he will figure all this out on his own and recognize.