What do you want? Do you want to end your friendship because you no longer respect this man? Or do you want to confront him in the hope that he might change something about the situation? If you can answer one of those questions with a clear, firm "yes" that seems like you've got your answer.

If you can't, maybe you could take a different approach altogether. Send your friend a note asking to meet somewhere neutral for a coffee and a talk. If he agrees, when you have the talk just tell him that you value him as a person and you value his friendship. However, you can't respect the way he is handling his relationship with the young lady in question. Tell him that because your feelings on the matter are so strong and becauese they are affecting your friendship, you are asking him to agree that this particular subject is off the table. You don't want to discuss the girl or his relationship with her and you won't spend time in their company. You may actually find it a relief to have forbidden yourself from discussing this situation with him. He obviously doesn't share your point of view. That doesn't make him a bad friend to you. It just means he may not be the person you thought he was.

Good Luck,
Hippiechick