I've had a couple of friendships that I had to walk away from. One person was manipulative to the point of being abusive, but because she had been abused as a child and an adult, I thought if I was a "better" friend that it would help her. Unfortunately, she just wanted to take everything that had ever happened in her life out on me. I let her move in with me so she could be closer her job (where I also worked and where we met). She was supposed to stay for a couple of weeks until she got her own apartment; three months later, I had to ask her to leave, at which point she became even more abusive.
The other "friend" liked to drink ... a lot, and she needed someone to chauffeur her around; again, I thought we were friends, and it took a while for me to realize that she only wanted to get together with me so she could go out and drink without getting arrested for DWI ... again. I tried to help her. I offered to be a buddy when she went to AA; I tried to plan fun things for us to do that didn't involve going to bars or clubs or parties; I gave her job leads when she lost her job; I gave her rides when she lost her car - none of that mattered. I was a "bad" friend because I wouldn't do what she wanted when she wanted. She was (and may still be) an alcoholic, which means she had an illness, but I couldn't take the abuse she handed out when she was drinking (she was a lovely person when she was sober).
The interesting thing is that my other friends - people I had known for a long time - did not like either of those friends, and they tried to tell me that I was being mistreated, but I didn't want to give up on people that I honestly thought were my friends. It was painful, in both cases, to realize that those two people were using me. They were in my life at different times, and they never knew one another, although, in hindsight, they were very similar personalities, and they probably would have gotten along well.
In both cases, I simply stopped interacting with them socially. I wasn't rude to them (I didn't hang up the phone when they called, or slam the door in the one friend's face when she came to my house to ask me face-to-face why I didn't want to go out), but I stopped going out with them, declined invitations to their respective homes, and stopped inviting them to my house. Once they realized I wasn't going to be at their beck and call, they both became angry and tried to provoke me (that's the only way I can think of to describe it) into socializing with them by accusing me of being a bad friend for not going out with them. Again, it's interesting that they both used the same technique to try to continue our relationship.
The one who had moved in with me called me more than a year after confronting me about being a bad friend; she spoke to me as if we had never lost contact. I was polite, I asked how she was doing, I wished her well, and then I got off the phone. The other person attempted to contact me through a mutual friend by asking that friend to tell me to call her; I didn't, and I never heard from her again.
I learned a lot about true friendship through those situations because my longtime friends showed me, by example, what real friendship is; however, that was a painful lesson learned.
🙁