believer

To 827 - To fix a relationship it takes 2. And both need to acknowledge that something isn't working right to "fix" it. If your husband is not willing to acknowledge that there is a problem ( the other woman) then you 2 can not work on the marriage.

However, you can work on you. YOu can go see a therapist to help sort out your feelings - hurt, anger, fears, etc. Find something that makes you happy - look back at something you used to do before you met your husband that brings back memories & do it.
If you can better yourself & make yourself feel good - it will help your battered self esteem. ( which I am sure has taken a hit) But remember this not about you - don't blame yourself ( I know it sounds silly & will be difficult not to do now) But trust me - he has made some very poor decisions but you are not to blame.
Who knows what your husband is looking for - he probably doesn't know. But you can be damn sure what he found in the other woman won't last & is only a temporary band aid to his issues. If he doesn't get to the root of why is got involved with someone else - those same issues will resurface later.
Good luck on the weeks/months ahead - keep us posted