Do you ever push people away?

Why do I push people away? Why am I afraid to get close to people? I seem to push people away or get bored of them easily. Why do I do this?

I'm a private person most of the time. I don't like sharing more information than I need to when I'm talking to people but most of the time, I am anti-social or really shy. I have no problem talking with people. It's just when people get too close to me, I get flustered and I space out. Then I push them away. I grow complacent and I realize that I have completely ignored that person. It turned out I was pushing away everyone and would not let anyone in my life. I think it stems from a fear of connecting with someone emotionally when I know that this can be thrown back in my face. I've had a relatively normal childhood (no scarring abandonment issues or whatnot), actually a pretty good one but for some reason I still push people away. So being this way makes it hard for people to get to know me because they think I'm either shy or really stuck up when they talk to me.

My greatest fear is not being alone but being hurt. I guess I'm just afraid of getting hurt when I let someone get close to me. Letting go of the barriers I build around myself is one of the most prominent issues in my life at the moment.