I thought I’d throw my two cents in here, in case ya’ll are interested.
I, too, have had friends that needed cutting off. As a female, I’ve always had problems doing that because I didn’t want to hurt that person’s feelings, or I felt partly responsible for the problem in the first place, whether I was or not.
Here’s a very extreme example: When I was in high school, I worked on a summer musical and there happened to be this guy there that was much older than me. He was nice, and I enjoyed talking to him while we were building - he was smart and we both had somewhat similar interests. But I never felt anything for him other than friendship - if we ever hung out together, there were always at least 5 other people from the show, and we never talked alone for more than 2 minutes or so, which was fine with me. After a while, though, he started calling me at home, asking me out for dinner and just generally started acting as though we were dating, on the set and when he called me. I already had a boyfriend, and he knew this. In fact, at the time, this guy had met my boyfriend and knew that my boyfriend and I had plans to marry out of high school (which didn’t work out, by the way, thank God).
Anyway, this guy was really invading my space and clearly getting messages I wasn’t sending. I felt as though my being nice to him had somehow encouraged this behaviour in him, and felt that I was responsible for whatever feelings he may have had for me.
Finally, I managed to get him to leave me alone. I was really mean when I did it, and I felt almost unbearably guilty afterward, but it was very necessary. I had gotten to the point where I was afraid to leave my house for fear he’d find out where I was and show up. This was clearly not a healthy friendship - it was getting closer and closer to stalking. Unfortunately, my boyfriend was oblivious. No wonder we didn’t marry. 
Like I said, this is a very extreme example of “friendship gone bad,” but I feel like there are lots of layers to women’s relationships, and guilt is also usually programmed into us (or at least it was programmed into me) at a pretty early age. As a female, when I have a problem with someone, I can’t really articulate it because I don’t want to hurt any feelings, and I often feel as though doing something that might hurt someone’s feelings is like putting my needs before theirs. So it’s difficult. Ending a friendship can be a lot like dumping a significant other. It really blows. Even with this guy, I agonized over telling him to fuck off for almost a year after this behaviour started, even though he was largely responsible for my quality of life declining (I was having problems with my BF at the time, too). Finally, I just freaked out one day. In retrospect, I’m really glad I did.
