My ex-boyfriend and I were best friends since freshman year of high school, and during senior year of high school, he confessed to me that he had a crush on me since then. I, however, felt the same way. So, me being blinded by his adorableness, I went ahead and took a step forward with him.
If that happened to one of my guy friends at this time, I would probably reject. I can't risk myself in losing a best friend like my ex. So, it would be better to keep the relationship we have now instead of taking a risk and taking an extra step forward. It's better that way, imo.