Dating your best friend, who you once were not attracted to, but now have second thoughts?

Hi, lately I been having second thoughts about dating a guy. We were best friends for a very long time, and he use to have feelings for me. I decided not to date him because I did not like him at the time, and was afraid to get into a relationship with him because I did not want to ruin our friendship. I also knew that if I did date him, we might of gotten serious because he was such a great friend I thought he would be a great person I might marry someday. Being young and afraid, I decided not to date him and jumped to fun relationships. Now in my mid 20's, were no longer as close as friends but we are still good friends. After dating a pool of men, and at a point in my life where I am ready to have a serious relationship...I think about him time to time (what it would be like to date someone like him). When we were younger, he would jump through hoops for me to make me happy, and treat me so nice. However, I was not attracted to him. Still today, I have doubts because we have not seen each other in a while and he has dated other women. He is single now, and I am single now but I can not help feeling what it would be like to date him. I definitely did not have that "spark" I do with other guys, but when i did follow those feelings it led me down to heartache. My bestfriend and I are great friends. We think alike, act alike, and as far as the 12+ years I have known him, has enjoyed his personality a lot. My family likes him, my friends like him, and everyone wonders why I never dated him when he was head over heels for me. Now as I am older, I am wondering the same. I am still scared however, that if we date, it might ruin our friendship if we were to break up. What happens if we do date, and I find that I am still not attracted, or I end up being attracted to someone else and ruin our friendship? I am not sure what to do. Has anyone ever been in this situation? I really love my best friend...and if I did date him he will be a wonderful bf like a wonderful friend he has always been to me...I know that if we were in this relationship, and if everything worked out, we would be one of the couples that would love each other unconditionally...however the feelings that I am feeling, I am not sure if it is really in that way that other lovers do....please help...