A few years ago i started a new job and very quickly became good friends with a colleague. She sought me out inviting me for coffee, hanging round my office etc. All was good for a few months and then I did something she disagreed with (although she didn't tell me at the time). She started to cool the friendship, without telling me why, until she became outright nasty to me. Luckily i changed jobs and so no longer have contact with her. I know that she has behaved in a similar way to at least one other person: one day they are the best thing since sliced bread and then suddenly she's pointing out all of their character flaws behind their back.
My question is not about her but about me. We both work in the same industry so I occasionally hear news of her and she seems to be able to maintain normal friendships with most other people. For some reason I have this nagging voice in my head that pops up occasionally and tells me that if i'd been a better person then she wouldn't have fallen out with me. Why do i feel bad like i failed at the friendship even though she was a bitch to me?