Scared of commitment?

As far as high school is concerned and guys and what not, I seriously think I have trust and commitment issues. I've never actually had a real relationship- but Ive had plenty of crushes. In every instance we start talking and let's say he asks me out, I make up some lame ass excuse and stop talking to him. It's happened numerous times and I'm honestly unsure why. I'm currently a sophomore- I'm just wondering if anyone else has ever felt this way