I think that you have to start by finding some positive things around you.
Understanding WHAT you are dealing with will bring you closer to detaching.....
Doing things FOR YOU and NOT in spite of him.
Finding a balance within, one that allows you to be you and not worry about affecting the relationship or him , or trying (and focusing) on splitting apart the affair.
Dwelling on what is good instead of what MAY happen.
Let's start there ?
We are here to help you, but YOU need to do the work.....