Cross-Sex Friendships

So one of my best friends ever is a guy. We've been good friends since high school. The only time we drifted apart was when he dated one of my friends. She was just jealous that we were so close of friends, but once they broke up we started hanging out again. This past summer we hung out every day. I always had people ask if we were dating.....which of course I said no, that we were just friends. What surprised me was that even my closest friends were asking me constantly. I guess it did kind of look that way since we saw or at least talked to each other every day, I visited him at work sometimes, plus we play around with each other all the time. He's always been such a good friend to me. He's always looked after me since high school, talked about my problems with me, and called me as soon as he came into town from school, even before visiting his mom first. We grew to be so comfortable with each other. Some of my friends would say that we acted like an old married couple already. I guess they said that because we would know what the other was going to say or react.

As the summer progressed, as well as the teasing from my friends, I didn't see him as the brother I never had anymore. I started to become attracted to him. There seemed to be some sexual tension between us.

With all that we've been through, I wonder if it is possible to keep a cross-sex friendship like ours.