Good luck asking the question. It's so hard to trust a S who has been unfaithful. I asked my H that question several times and he always answered it was over--but it wasn't. He became an amazing liar.
He said that what made him stop lying was my calling a L to file for D. He was scared back then, and promised to be faithful. But when I asked to have access to his cell phone account, he hated it. I actually found some old lies he had never come clear about. I found myself checking his calls every day. It was awful. I'm not sure how to best approach these kinds of stich, so I'll be interested in hearing what other people have to say. My advice would be: time. Only time will allow him to stop the A and to both of you to trust each other again. But he must stop the A. Good luck...