I think I'm in love with my best friend (of the opposite sex.)?

Okay, I know there's always a lot of questions like this, but I guess every situation has its slight differences. So my best friend is, of course, a guy. We really only became best friends because he was good friends with the guy I liked, and I was good friends with the girl he was dating. So we started talking, helping each other out. Until the guy I liked, well, that just didn't end well, to say the least, and his girlfriend dumped him. And when all this happened, I was worried I would lose my best friend, because we would no longer have anything to talk about. But we just became closer after that, and helped each other through what happened. Now it's a couple months later, and I recently realised that I have feelings for him. But I don't know how he feels about me, and I am so scared of losing what we have. I really care for him, and think I may love him, but I don't know if I should tell him how I feel. Should I just leave it? Move on and not risk the friendship?