So he's engaged...?

Almost a year ago I started noticing a very attractive man who worked next to me. We started chatting often when we ran into one another, and then one night had a ual encounter in his office completely out of the blue. I knew he had a girlfriend, and I'm not normally the type of girl that would partake in that sort of behavior, but with him I just couldn't help it. Our encounters continued often, and then he told me he had asked his girlfriend to marry him. The thing about it is we've become extremely close...he's now one of my best friends. I have extremely strong feelings for him, and I know he has feelings for me, but even if he knew I was a better match for him than she is, I don't think he'd want to sort of start over. We haven't been having or anything of the sort lately and has really just become an amazing friendship. I just don't know what to do, I guess. In a way, it'd be easier if I knew he didn't feel the same way about me, but I know he does.