With friends (don't even get me started on relationships... I'm scared of being on them for this same reason), I'm very protective because I love them, but I often forget they're human being with flaws and B&W thinking happens.
They do something (not to me) in their lives, a mistake, I get disappointed in them and I start to see them differently and, in a attempt to avoid getting more hurt and disappointed in them (this happens a lot), I stay away from them, even though I miss them, I can't help but remember ONLY their mistakes and flaws and think "how could you? I thought you better than that. You're not the same to me anymore"
That's why I avoid relationships, I can't handle their past and I'm scared of getting hurt in the future.
The thing is, what hurts me is mostly common mistakes of people, exaggerations in sex, drugs and drinking. I'm very self-destructive also, especially when I'm disappointed and sad and angry. They turn into a bad person to me.
I need to stop and accept them and realize it's not always 100% good OR bad, but I get impulses to run away from them.