Why would guy show interest in married woman?

An coworker who I am on good terms with has been indicating he's interested in me. Eye contact, body language, long talks. Nothing too forward though. Trouble is, I am married.

He has not been too forward or acted sketchy. He's just been signaling he likes me and is interested. However, I'm not sure why, as I a married.

Why would a guy do this? It's like he wants me to know, for some reason.
Why would guy show interest in married woman?
Post Opinion