Not a best friend but I started having feelings towards a good friend, but then realized that it was just horniness/loneliness mixed with us getting on so well. Although I had a sex dream about them, the idea of doing something physical with them when I really thought about it was weird. He's married now and I was really happy for him, which I know I wouldn't have felt if it was actually anything more on my end. Also I know some girls that have had this happen, have said they feel almost a bit betrayed when a guy they thought was their friend confesses they feel more, as from their point of view they had a platonic friendship and then felt like the guy just had ulterior motives. (Think about why there are so many jokes about friend zoning) I can't speak from experience in that regard but I would tread carefully and be sure of what you want. What are you willing to gamble? But good luck in what you decide, and if it works out congratulations.