This this guy at my college and I've known him for a few months now and a couple of weeks ago he asked me out. I told him id think about and I didn't know but now he keeps asking me and the truth is I don't really want to go out with him. He's a really nice guy but I only think of him as a friend. I don't know how to let him down without hurting his feelings.
Any advice?

Are you going to let yourself down instead? Be honest but politely tell him you want to be friends first. If he isn't mature enough to accept this, then you're better off without him in the long run.

You need to be honest with him and tell him that while you like him, it is as friend and not potential boyfriend. To not tell him your true feelings is not fair to either one of you. It is always better to be honest with these kind of situations than give a false hope of something you are not prepared to follow through on.