help, I've developed a crush on my friend/coworker! *edit*

So he was one of my first friends when I started working there. We've hung out everyday at work and recently we've been messaging away from work (talking about work, music and tv shows). We like a lot of the same things and I feel like I'm developing a crush. Big problem, we're both taken. I don't know what to do, I can't stop thinking about him. Advice, anything?