Time.. he has to build trust with you, you have to learn to trust him.

If you can't then close the book and move on!

Trust isn't something that is given or taken - it's earned.

So I agree, it takes time. And it will be little things over that time that will rebuild the trust. Don't run bullshit tests. A lot can happen if you can put the hurt aside for a while and not use it against him. Be his friend again.

I am in a similar situation and (after one sucky summer which started with my dad dying and ended with me finding out my wife slept with buddies) I have had to "get over it" and be the bigger person after all she has to live with her actions and my concience is clear.
If we had no kids I would have walked but divorce with kids not option for me(when i said for better or worse i meant it)
I do not trust my wife so cannot help there.
I really like the other two responses.
JJ

a wise woman once told me, "the only thing i can safely trust is my ability to handle what you say and do to me"
when you fully trust yourself then the fear goes away and the love (if it is still there)remains.
this is a toughie. but communication and honesty are key.
you can never be SURE it will not happen again, but obviously, right now, he is making amends.
and that's all we really have isn't it, right now?
blessings!

It is really hard to cope with this kind of hurt. I went through a really bad patch a few years ago and right when I needed my husband he decided it was his time for his mid-life crisis, got a girlfriend and proceeded to have a very public affair for 3 years. In your case it sounds like your hubby hit that age where they freak out and wanted to reclaim his youth. Even if he didn't cross any major lines he still let you down in a huge way. My advice to you is that if you in your heart of hearts want to remain in your marriage you will need to put down in a safe place all your anger and resentment and see what happens. Neither of you will be able to go forward if the elephant in the corner is too well fed, it takes up too much room. Trust is a hard thing to win back and forgiveness is hard to give. it all comes down to whether or not you want to remain married. if you don't then don't drag it out fighting every night because that will make every member of the family hurt but will not ease you pain. Good luck.

This is relatively easy my dear. You remember why you married him in the first place. It wasn't because you knew things would be perfect. It wasn't because you would always get your way. It wasn't because he always knew what would hurt your feelings and avoided those things. It wasn't because you could see yourself always approving of his choices or actions.
See where this is going? You have to consider that you have not always been perfect to him either but he's still there. Men handle stresses drastically different than woman do and sometimes, we make mistakes with our handling of those stresses. It doesn't excuse the complete lack of concern for your feelings, but perhaps he felt that you weren't concerned about his feelings either. As for the trusting him, you don't really have a choice that you'll like in this instance, but you do have an obligation. "In good times, and bad. In sickness and in health. ETC..." Sound familiar? You have to remember that the vows you made to each other aren't overlooked for one when the other screws up. You have to trust him or you'll drive yourself mad with speculation. If he hasn't cheated on you in the past, it's likely that he didn't this time either. If he has cheated on you in the past, then you already knew he had a tendency towards this behavior and decided to stay with him anyhow.
Don't take what I'm saying to you as an assault or anything like that, it's just that you put it out that you were serious and as far as my response to your posting, I'll be equally serious and direct. You deserve that, don't you? :P

Staying in a relationship just for the kids teaches them the wrong idea. You have to WANT to be able to trust him and only you can decide if that is possible. There are some that can forgive and there are others that cant. You choose which one you are capable of being and be it. Once trust is lost it takes a lot of time and effort to get it back. It will not be easy.