Three ones stand out:
1) Erin - She was my best friend since 8th grade. We had quite the roller coaster friendship. Lots of highs, lots of lows. We were at our closest freshman year of college after her mother passed. I was really her strongest support in that terrible time and we had worked through all of our difficult history.
Sadly, Erin and I started to go different directions. After her mother died she lost all motivation to do anything with her life. Her mom, to Erin's credit, was an amazing woman and an amazingly positive force in the lives of anyone she knew, including mine (I mourned her death deeply and my father even did the service). Erin turned to drugs, I was devoted to my own goals. I tried to stay friends with her but the people she got involved with....let's just say it got to an awkward point were we had little in common anymore. I still miss her.
2) Stefanie - A very close friend in college. One of my three or four closest. I loved her to death but she was very self centered in the purest sense of the term. She was so wrapped up in herself that she was oblivious to who got left in her wake. In a couple of months time she had slept with the boyfriend of one girl in our group and the ex of another. Everyone kind of turned on her and one night she IMed me asking me if I hated her too. I told her I didn't, though I was appalled by the things she'd done. She started saying things like, "I just want to jump out the window" so I hauled ass over to her room.
I found her hysterical, talking about suicide, and tough love Lilly came out. I pulled her off the floor and commanded her to get some things together to stay with me that night. she didn't want to, so I threw some things in a backpack for her and proceeded to drag her halfway across campus to where I was living. At this point I realized I was not equipped to deal with the situation - I could stay up all night and watch her, but then what?
I talked to my RA and told her Stef was suicidal. She called campus cops. I felt like Judas but, as I told Stef, "I'd rather you hate my guts and be alive." She as taken to a hospital for evaluation. When she came back the next day she told me she understood and forgave me for what I did, but things were never the same after that. I don't regret my choice.
3) Stephanie - (with a PH) This the only time I have consciously chosen not to be friends with someone. When it was just me and her, the girl was a blast and true to the end. I could count on her for anything. But enter a guy into the equation....let's say she had some severe self esteem issues that she took out on me on a regular basis and my endless well of forgiveness and patience finally, at one point, ran dry. I bent over backwards for this girl to try and make sure she never felt bad about herself around me, but finally I reached a point where...enough was enough.