new man at work, ever perved at man while in a relationship?

Have you ever looked at another man while you're in a relationship and thought holy shit you're the most attractive man I've ever seen?
Recently a new guy started working as the PE at the school I work at, he's covered in tattoos, muscles and has a very attractive smile.
He's son who's 6 is in my class so I see his dad a lot but I can't help but perve on his dad every time I see him. I would never cheat but I can't be the only one who's guilty of having a bit of a perve