I haven't been on here in a while, but I agree with the OP. I did the "Little Bo Peep" for the first 2-3 months after finding out about the A, which only seemed to increase the lack of respect and outright hostility toward me by my W.

I recommend an aggressive (but respectful) approach on ending the A as soon as you find out about it. Don't call your SO a slut/jerk/etc. but stay above the gutter and say what you think is right.

"You can't reason someone out of a position they didn't reason themselves into."