I'm really bitter towards my ex's girlfriend, how should I deal with it?

[Carl]

You have more issues than he. Grow up a little and mature yourself. Only one thing is certain in this world. 'Change'. We all change, we all have to deal with the changes of others. If you desire a b'friend that has no other female friends, then you have already lost the b'friend. You will have to get over the in-securities and be happy with what you have, not dwell on what you don't.
Next quit that group. Why in creation are you spilling your personal life to a group just a experienced as you are? Make your own decisions, live your own life. Keep personal things personal and private. If you need advice, ask one who has the knowledge and experience to provide that advice.