It sounds to me like your husband was under an enormous amount of stress. Not being able to cope, he sought to escape his responsibilities and his feelings through a brief fantasy that he could turn back the clock. He got to the brink of losing everything and then came to his senses. I’m guessing that he is full of regret and doesn’t know how to win back the trust he so thoughtlessly threw away. It would be equally senseless for you to throw away what has been a good marriage in the wake of a lapse in judgment that occurred under such stress.
You are right: You don’t want to spend your life looking over his shoulder. He can’t spend his life feeling his wife doesn’t trust him. From my point of view, you two need couples therapy for awhile, not individual. You both need to gain some understanding about why your husband didn’t feel he could turn to you when things got so hard for him. He needs to help you gain confidence in him again. You need to feel safe in your marriage. That can’t happen in separate offices across town from each other. I think you would be better served by using the safety of a couples counselor’s office to delve into your feelings, to forgive the past, and to learn new ways to be supportive of each other. Thirteen years of marriage and 5 kids are worth the hard work of improving your relationship.
I wish you both well.