You may be feeling guilty and trying to come to terms with it.
Did your husband do something for you recently that may have left you feeling unworthy?
Have you been thinking of telling your husband about the affair for some reason?
It's a double edged sword. If you tell him to clear your conscious, then your hurting him, and then re-hurting yourself and possible ending your relationship. If you don't tell him and he finds out from someone else,you both still wind up getting hurt.

I hope I could help,....even a little. Good Luck!