I'm so ashamed to admit this
What are ashamed to admit to me?
It was anger, I was really angry with someone. I'm really ashamed
If you did something you're ashamed of then you should get it off your chest. The guilt could make you feel worse.
I'm so ashamed to admit that I had an affair with my best friend's husband
Well then, I hope you now know what you did was wrong and having an affair was not a good thing to do, and your best friend's feelings will be hurt if she finds out. I do hope that you should stop having an affair with her husband and just mind your own relationship so that you don't ruin your relationship any further.