How do I get over a gay crush on a straight coworker?

So I'm a 20 year old gay guy. Im only out to 3 of my closest friends. About 6 months ago I moved across country and started a new job. I work in a small tv station, with about 3 other people. One of the guys i work with, G, I have unfortunately developed a huge crush on. He and I get on pretty well and we spend quite a bit of time together at work, occasionally going out together to do fieldwork and stuff. He makes the occasional gay joke about himself, and can get almost a little flirty with me, But I know that the crush wont actually go anywhere because i'm pretty sure he's straight (he has a girlfriend who he's been with for close to 5 years) but its becoming increasingly painful, having to work so closely with someone that I have these feelings for. I find myself thinking about him all the time now, even when he's not around, and actually get quite sad if i get into work and he's not there. I'm getting to the point where I just want to stop liking him and move on, because im pretty sure that nothing could happen between us.Any advice to help me get passed this would be great, Its hard to distance myself from him when I have to work so closely with him.