You can go to counseling, it may help you cope with this in the mean time. It will NOT stop his affair and help from a counselor will be limited as long as there is deception and a third person in the marriage. But, it’s better than doing nothing.

Gather your evidence and confront him. Make your
boundaries well known and demand what you need. Protect yourself and your assets together before you do this, as he may not play fair when it all comes out. Many an affair falls apart when exposed. He enjoys the attention, but may not really want to lose you either. He may not “love” the other woman either, but will play the game and tell her what she wants to hear to keep it up. The amount of fantasy and lies involved in this kind of thing are amazing.

Look for a counselor certified in couples counseling, with experience with infidelity. Marriages can survive an affair, but it will take lots of work from both of you.

Resources
A few good books:
“Not Just Friends” by S. Glass
“Surviving an affair” by Dr. W. Harley
“After the Affair” by Springs

A yahoo group that has many helpful articles and links in FILES. Not a good support board, not very active. But, loads of stuff in files. Simple to join.
A few other helpful sites:

A few good support forums for those dealing with infidelity. Lots of helpful people who have been through this trauma.

An ebook written for the wayward spouse to help them understand what they need to do to rebuild from the damage they created:

Some marriage weekend programs:

If he’s in love with someone else, counseling’s not gonna change his mind. You don’t deserve to be with a man that cheats on you and can’t give you his whole heart. I think it’s time to let him go.

If he loves someone else it will not work. Would you really want him to stay?

Of course not. Because you need to be in love to have a sane relashionship. Move on, I know it is hard but whe the love is gone, there’s nothing else to do.

if he won’t admit it then there is a chance that it will still work with the two of you. However he needs to be honest and to prove that he is through with her. As it stands now, he is lying and it will never get better from there…..until he comes clean.

And you know of the affair how?

I would cut your losses and find someone who loves you, not some hussy in his office…………JERK!

So sorry your husband has no character. He made a choice to have the affair. Counseling is a venue to work out things when both parties want to make the marriage work. If you have children let him tell them why the marriage is breaking up…I wish you the best…

First you have to find out if he really is in love with her, or if its simply an office fling. If he is not admitting to it then it could be because he loves you and does not want to lose you over a cheap thrill. And if he agrees to counseling then there is your answer, ” not willing to lose you over something that maybe did not mean anything. So try and get some facts and dont go based on gut alone.

People have “affairs” because their needs are not being met. Do not look to deep into your husband’s infidelity for the truth of the situation. You will find the problem lies with you. This does not negate his responsibility within the marriage and his lack of restraint only proves his weak, immature and selfish character.
It was always there and you chose to overlook it. Hard to overlook now.
Counseling will only work if the person is willing to look at themselves and accept responsibility for their actions.
Ask your husband the one question that will prove the efficacy of counseling - “Do you want to be married to me?”
It’s a yes or no question.