No matter how you slice or dice it, having sex with a married man is wrong nothing you or anyone says can give this fact any justification, what you're doing is wrong, morally and every other which way, you're a spare or 3rd in a marriage and marriages don't have spare, if you want to regain yourself respect and dignity then do the right thing, not by him not by you but by the woman who in all of this is totally innocent, HIS WIFE.
All you're getting is left overs, are you that desperate you'll settle for that.?
HES A LIAR AND A CHEAT, don't allow this man to drag you down with him, he doesn't care he's getting it all ways, but if you can't see this then more shame on you. Sorry, but who would condone such behaviour.