Originally Posted by Moonmama
Basically, she already knows so I don't see why he is so scared to say something...
Because HE feels what he's doing is wrong and doesn't want to either lose her, or have her be mad at him or have her see him as a liar and a cheat.
He wants to do whatever he wants, and have no repercussions from it. He knows if she KNEW what was going on (yes she might know deep down, but I mean out in the open knew), that he most likely would lose her. And so it's easier for HIM to get what he wants by lying to her.