Hot for another guy?

Have u ever been sexually attracted to someone else like a coworker or a friend or something? It's a guy that I work with and we kind of flirt with each other a lot nothing bad just chit chat and a lot of giggles. But I find myself thinking of him a lot, sometimes in a sexual way. Some of the things I "like" about him I love in my SO. He knows about my SO & I think he's in a LTR as well.
And although I say I'm sexually attracted to him I would def never cheat on my SO. I just don't understand why these feelings and where they came from.
Help ladies lol