I WANT [MY] COWORKER... HOW CAN I TELL HI[M] | 2016

Hello Reddit, It's my first post so excuse if its not proper. I will make this short and simple. I am a gay male and I am out so here at work everyone knows my preference. Well I have a thing for my Male coworker I want to suck him up or let him fuck me. Now I have a nice bubble butt and you can tell. He knows it too. And he is an ass man but he is straight. We get along very well. He Is such a great guy and he does have a girlfriend whom he lives with and a child. We joke around a lot and throw in little dirty jokes. I don't know if I should tell him that I want to mess around with him or just keep it to myself.. I don't want it to be awkward with one another. I have had dreams of him and I messing around. I really enjoy the dirty little comments we say to each other, but I think that he is just an open minded guy and he feels comfortable with he's sexuality, that's why he jokes around with me. Please help... What should I do?? BTW I have a boyfriend which is why I am keeping it all to myself and not mention anything.