You just need to cut off being friends with him. If he doesn't respect his wife enough to remain faithful and end the relationship before pursuing you, why would he respect you and be any more faithful to you?
Seriously? You have to ask what he wants? He wants to stick his penis in you, and for you to tell him it's OK for him to cheat. Duh.
Whether or not he has actual feelings for you is secondary, because he isn't considering your feelings and desires for honesty and integrity. He wants you to empower him to do what he knows is wrong. Don't let him use you like that.
"Well, then," the Cat went on, "you see a dog growls when it's angry, and wags its tail when it's pleased. Now I growl when I'm pleased, and wag my tail when I'm angry. Therefore I'm mad."