Most Helpful Guy
Honestly, you should just bluntly tell him you aren't interested. Be nice about it, but don't give him the "nice guy" speech. Depending on the severity of the crush, it might cause him to linger around and think there's still a chance.
Guys don't tend to want to settle for the consolation prize of being friend zoned.
Most Helpful Girl
You're a really nice guy, and I think you'd be a great boyfriend to someone, which is why I've been seeing you. However, I can't seem to feel a natural attraction to you or spark with you. I'm sorry but I don't think we can be anything more than friends.