Why is that I say no to a guy or I'm too busy, they keep pursuing me?

This guy has been trying to ask me out but I said I'm too busy and I'm about to be a senior. I don't understand why he likes me to much. I'm a dork. I live drawing, comics, whatever. I mean I do like this guy a lot and he is a good guy, and HANDSOME. I don't know about this dating thing. I feel like I'm pushing him away. We bumped into each other two weeks. He admitted he had a crush on me in middle school. I really like him but I don't know. He really likes me a lot.