Hi, I'd like to help you with your question.
I am sorry you are in this situation with your marriage. It is hard when trust becomes an issue and rebuilding a marriage takes a lot of work.
It sounds like your husband is having trouble breaking off the affair. This is not a good way to help you rebuild trust in your marriage. He needs to hold his end of the relationship and be trustworthy before trust can be rebuilt. That is why you feel your efforts are not making any headway. It is also why you feel full of fear and doubt.
I would highly recommend the two of you seek out couples counseling. He needs to break the relationship off and begin working on your marriage. Until then, nothing is going to work. Talk with him about finding a counselor then make an appointment. You can find a counselor through your family doctor, the local community mental health center, or if you attend church, the pastor is often trained in marital issues or they know good resources for referral.
Meanwhile, you can help yourself by spending some time away from the stress of the marriage issues. Go out with friends, pamper yourself or browse a bookstore. Anything to help you get your mind off the problems and stress. This also helps you gain new perspective and may help you come at this problem with better insight.
Some books that may help you are Should I Stay Or Go? : How Controlled Separation (CS) Can Save Your Marriage by Lee Raffel and Hope For the Separated: Wounded Marriages Can Be Healed (Chapman, Gary) by Gary Chapman. You can find them at Amazon.com or your local library may have copies for you.
I hope this has helped,