Most Helpful Girl
Talk it over with him, let him know you're falling head over heels in love with him. Tell him you've noticed him turning up the flirting, ask him if he is feeling more than friendly?
I married my best friend a little over two years ago, it was the best thing we've ever done together! We've known each other since five and six years old. We went from playmates to friends, best friends, BFFs, flirting friends to friends who totally fell for each other! Before that first date, before anything started we sat down and had a long talk. We talked about how this was going to change our friendship forever, how we would remain friends even if we couldn't love each other in a romantic way. Thankfully we've never had to worry about those reservations because friendship is a great foundation for a relationship.
So if he's up for it, take the chance you'll never know if you don't!
Most Helpful Guy
You've known him for a long time, so the risk of losing him from your life completely is lower than for someone you just met. Your criteria for him should be the same as for any other guy you want to date, and you have the advantage of knowing him so well that you don't have to wonder if you're seeing the real him. I say go for it!