well in my opinion, for a relationship to really work out.. longterm, you have to be best friends. I think anyone who's married, should be/is married to their best friend. Allthough its hard to go for it.. you gotta weigh out the pros and cons.. the way i look at it, you win some, you lose some.. you just got to decide if it means more to you to go for it, or to let it pass by.. (maybe for something in the future)
but if they really are your best friend.. then even if they aren't interested in dating you.. they won't let the friendship go to shambels.
but i can tell you from experience... its great dating your best friend
hope that helped a bit
good luck