If they don't make me happy. That's my best answer.
Alright so this is all an example. Going with the example, that it's all my fault, why does it all make me feel horrible? Why would I be sad losing a friendship if it was my fault? Well, there are a lot of reasons and this can all go in a big circle, I'm just writing because I'm confused.
I think I have expectations for my friends; as I would a boyfriend. I think these are based on past friendships. What we want and don't want. You know within a short time if a person of the opposite sex would be compatible with you, I think it's the same with friends.
Soooo why force a relationship that you know is against the odds to work? Good question, people are unpredictable, so we may never know.