How Do I Tell Him?...

I have a friend who I really like, and he wants to go out with me...I like him but I dont want to go out with him and ruin our relationship in the long run because it happened before...I want to tell him this, but without hurting his feelings or making him feel that I am totally not interested. Can anyone help me think of a good way to tell him this?

Thank you Ken...I am sure he would choose friend over nothing any day...It is just I want to be sure his feelings arent hurt...Because after I tell him this his feelings might change toward me all together. I dont want to risk messing everything up. I hope he understands. Thank you for your advice. xxx

Any other advice is very much appreciated.