I have been with my husband since i was 15 yrs old ...

Hi,
Sure you were deeply hurt.  Yes, your husband ruined the trust (and trust is one of the main pillars of good relation).  You have to decide: Do I stay with him or not ?  If you decide to stay than you have to forgive him with all your heart (that means totally forgiveness and never mention it again).  Please remember that forgiveness is a devine value.   As per your description I would recommend that you forgive him.... but you should have an open deep discussion with him.  Tell him how much you were hurt, how you feel about it, that you decided to forgive, and hope that he be smart enough and fair enough not to repeat his mistake..... make it clear that you won't forgive twice....   It won't be easy but you can bring trust back to your relations (specially if he helps you !). 
Best regards,

It's understandable that you have lost trust in your husband. I think you should seek out marriage counseling. I think through that, he will be able to get a better handle on how much he hurt you and how you've lost trust in him. Through marriage counseling, I think he will learn to be a better husband as well as learn how to earn your trust back. Good luck!

Trust is so easy to lose and so very difficult to regain so your reaction is totally normal. You can believe him and try to regain that trust, but it would be a good idea to start by you both going for counseling. Often a third party can see things in a relationship that neither husband or wife can. He has a few good things going for him: you still love him, he is a good father to your children and a good provider AND he is contrite. By giving him another chance once you both go through therapy you will have a lot to gain and much less to lose.

This happened to a girlfriend of mine and my heart breaks for you .   Your husband as broken the very foundation for which your marriage , love and respect stood for and it is UP TO HIM TO FIX IT !   My friend and her husband started counseling and when he saw the damage he had done to her as a person he loves and the respect she had lost for him , he completely lost it , cried his heart out their counselor at this point sat back and let it happen , it was a 2 hour session , the beginning of saving their marriage .  He was told by the counselor that it was his place to make sure his wife never felt pain again like he had caused her . And his life was now an open book to her , hide nothing , and make sure she knew where he was at all times , to ease her mind and help rebuild the trust .  My problem with your case is your husband saving he wanted to make sure you were the one ,  he should have already known that after 18 years , so his excuse to me is not a valid one .  Therefore I would get you both in counseling , think he's got something else going on with his less than realistic reason for cheating .   And I would be keeping my eye on him , check on him , his where abouts and so forth , show up where he is suppose to be .  He caused the distrust in your marriage and you should not have to live the rest of your life not knowing , find out .