Only three times have I ever "dumped" friends. Both were deserving situations... I make it a rule to not do that, but if it starts affecting my life, it has to be done:
1) Suicidal friend from High School... spent YEARS trying to help my friend out but towards the end of the friendship, it just got WAY too heavy for me, because she would try to commit suicide and then call me at 6:15AM on my way to work and tell me she took pills and vodka to wash them down. This happened way too often. It was purely for an attention grabber. She also insisted she could communicate with the dead--and that she had spoken to my grandfather, describing things that were clearly not him (although she wouldn't accept that when I told her). Yeah. After a while, I just had to say buh bye, because I found myself stressed and depressed over what to do with her. She was on heavy medication from a psychiatrist but never a psychologist to deal with her probs.
2) This girl that was my friend's friend. She had serious issues with growing up, and insisted if I wasn't gay we'd be together (no effin' way). I never really liked her, but was civil as she was my friend's friend who ended up just remaining friends with her out of pity rather than a decent friendship. Anyway, this girl, would continually try to flirt with me, touch me, and whatever, despite the fact that she knew I was gay and I NEVER once made any suggestion I was interested... AND, I already had a hag, so that role wasn't going to be filled.
3) A guy who's ego is off the charts... was a college roommate. Knew I thought he was attractive, and he played on that. Lied to me left and right. Walked around naked in front of me, simply to know he was making me blush. Had me hide the fact that he was cheating daily on his gf (and now wife), over and over. After his father died suddenly, all of his friends including myself hung out with him to get him through it, and he just became a complete impossible jerk after that, spreading rumors about people including me, etc.
Those three I said bye to, and I don't regret those decisions AT ALL. I know how much it can hurt when a friend kinda dumps you, but guess what, it happens to everyone. I lost my friend that I had been friends with for 21 years, because I told him I was gay one day, and I haven't seen or heard from him since. Yet, a year ago, my parents were invited to his wedding.