Most Helpful Guy
It sounds like you still want to be with him but don't think he would stick around if he knew everything about you. If you still have feelings for him sit him down and talk to him, then both of you together decide where its going to go.
Now IF you really don't want to be with him just pull the band aide off and get it over with. Tell him you just don't feel the same anymore and think its best if finds someone who will care about him the way he deserves. Do NOT try to be his friend, at least not until some time has passed and you both have had time to heal. Being friends with someone you are in love with but can't be with will keep the wound open.
Think long and hard about your choice, but once you make it don't look back.