Ask the Expert: how to handle a divorce (Part 1)

I found out my husband of 6 years was seeing someone outside of the marriage. He had been lying to me on his whereabouts for more than 6 months. Long story short, he's promised to cut ties off with her except professionally (they work together but on different teams). We are going to go for counselling, in hopes to help us both communicate with each other better. How do I learn to trust again? I can't get over thinking what if he continues to see her behind my back. He's a good dad otherwise. We have 2 below 5. And I told him I'd rather cut things off between us if he can't let go of her, since he's already broken his marriage vows.