Should i date my best guy friend?

i dont no if i should date my guy friend cause we are really close and i dont want to mess things up but he keeps bugging me sbout it and saying he really likes me but i am really in to this other guy but if i say no to dating him agin he is not going to be friends with me any more!! so im really confused! Should i say yes or no?? or try the other guy who has an on and off relationship at the moment but i have liked for a while?