For me - my feelings at the time about myself, him and our relationship is the reason WHY the affair happened .. can anyone BS or WS help me understand what else he is looking for ...
First, you are not looking far enough in.
The reason WHY the affair happened is because you allowed it too. You choose to have an affair rather then to seek other outlets for your hurt, pain, frustration, and confusion in your current relationship.
I think the reason why you cant seem to answer his question is because you still havent 100% owned up to the affair.
Once you let it sink in that there were 101 other ways to handle your situation with your spouse and life and relationship - then you can move forward in finding the whys to how you got to this current position.
I will tell you mine, so you might understand a little better maybe.
I thought the reason I had my ONS is because my XH and I didnt have alot in common. XH was actively ignoring me to play video games and he rarely if ever did things that I enjoyed doing. We lived as roommates and I was very starved for attention and I felt like I deserved to be loved and desired. I justified the affiar by saying that I deserved to feel pretty and desired and wanted because my XH wasnt doing that for me and he was Actively ignoring me.
The above is a bunch of excuses that SI'er would call me on and let me know that I am not going far enough. So....
The real reason I did it is because I wanted to and so instead of choosing counseling, seperation/divorce, or actually talking to my XH, I selfishly took away his chance of working things out like an adult.
In my 5+ years of working on myself, I also realized that i have FOO issues and things that i needed to work on that added to my ignorance of how to be in a relationship and what a healthy relationship really was.
I realized that my view of personal bounderies was very skewed and I usually did not think of how my choices would effect my partner at all. It was my way or the highway pretty much all the time.
I also realized that my whole life I have wanted/needed the approval from the males in my family more then the females, I looked up to them more, so impressing them was more important to me, Thus, recieving praise and affection from males in my life was also more important. This led me to the slope that allowed me to think it was ok to cheat on my XH.
I honestly never really learned how to handle relationship stress and the ability to figure out how to navigate tough issues properly, so I didnt have the tools to handle what i needed to handle.
I also didnt have the forethought to get help when I needed it....that relationships dont come with a step by step guide and that it was ok to ask for help when I needed it.
******
Your BS will ask why for a long time, always own the choice, tell them that it was because you were selfish and self centered. Get into IC and learn your FOO, learn what your slope was....and do a Timeline so that you can work on all of that.