I've been there too questioned it to the point where I thought they were always just in my life to use me for something they could take away from me as soon as they had my confidence.

I've always had my guards up with friends, I can't let it down.
I don't know if it was in my head but at some points in my life I've had friends manipulate me and back stab me, and just been plain mean to me.

I would stop wondering about it though because just because you had a bad run of luck doesn't mean its going to keep happening. All of my friends up until now have left my life and to me its a real bruise to my ego to the point where I didn't think I deserved to have any friends because something about me kept pushing people away. So any friends I encountered up to last year I always questioned why they wanted to be with me in the first place which in the end pushed them away leaving me alone; back to square one.

Just think to yourself you can't be that bad of a person if someone is willing to stop what they're doing to chat with you or want to spend time with you, the world doesnt do that. They want to be with you because there is something about you that attracts them to you and you should be flattered instead of putting yourself down. I've been there and trust me you're insecurities are all in your head, people DO like you for who you are so stop putting yourself down so much. You're a great person and I bet all your friends and family think so too.