Most Helpful Guy
Whatever you do, forget the "just friends" stuff. It's one of the most demeaning things a woman can say to the man who loves her. He's a big boy. He can handle the truth and the pain that goes with it. Just don't string him along because you don't want to hurt him because it will have the opposite effect.
Most Helpful Girl
Well honestly you can try to put it as nice as you can but in the end of the day a breakup is a breakup it still will hurt and regardless some people will still take it more offensively then others. All you can do really is explain to him as nice as possible how you feel. Only you can find the closest to perfect words that you can tell him to help him to understand.