Why can't I be forgiven?

I forgive all the time. People hurt me, do wrong by me and I forgive. But I make a little mistake and that's it. People leave. Seriously, WTF am I doing so wrong? I honestly don't get it. I am apparently cursed. Meant to go through life alone without anyone to care for me. I said I was sorry, and I mean it with all my heart.....but it's never enough and I'm left alone and crying...