@baseballchic,
My take is that you and ex have different views of what is going on here.
You see his girlfriend as a horrible shrew who doesn't understand you friend like you do. You see your ex as a great guy, wonderful, funny, etc with whom you share a great friendship and who would appreciate what you offer if he would only open his eyes.
Your ex sees his girlfriend as the possible love of his life. He sees you as a regular friend who he dated for a while, but who clearly wants something more and he knows HE IS NEVER GOING TO GIVE YOU THAT, so rather than lead you on or have you mooning around, he would rather just end the friendship.
Since life is not a Taylor Swift video and sometimes the best video loses anyway, it's time for you to write this one off and find a new guy.