Rebuilding trust after infidelity?

My husband caught me in a lie and found out I had been flirting with a co-worker. Nothing happened otherwise. But he basically considers me to have been cheating. I don't know if I agree. Anyway I was mad and put him down and said he wasn't attractive. I know I did wrong and things aren't the same. He seems depressed and though he says everything is fine I don't believe it. Now how to regain trust? How to get him back to being the strong and motivated man he was before? I'm sorry but I'm also tired of him sitting in his man-cave and reading the paper.