one of my best friend just confessed to me

i have no idea what to do. its not like I hate him but i just cant picture me and him in a relationship or me and him being together in the future. so the obvious answer should be rejecting him right? well yes, but what if I accept and then i eventually develop feelings for him? or what if I reject him and regret it I the futute? i wanna live my life to the fullest and not have regrets but its so selfish to risk a mutual friendship for my future well being. what should I do?