I struggled with the same thing for a year. Until I realized that it was okay. We all heal differently and need different things to make the situation liveable. So, I did what most on here would say not to do. I sent the OW a letter on Dday anniversary a year later outlining what I felt about her. I also included a letter my fWH wrote about how he regretted what he did to me, how he loved me, what I meant to him, and how he felt about her (which was disgust). Finding this site too late in the after A, we never did a NC letter. So, I guess in some respect it was a NC letter of sorts...just a bit more harsh.
And yes he does feel indifferent about her to all you fellow SI that are on that band wagon-I forced him to tell me how he felt if he didn't feel indifference. At that point in my healing-indifference meant Jack shit to me. I wanted him to HATE her. Even if me having that type of HATE scared him. I am the type of person, who always saw the best in people and surrounded myself with a lot of different people. So it WAS scary for even me. Now, I have reached pity for her.
But anyways...back to the story....
I needed her to be taken down a peg or two. Call me whatever you want, but I didn't start this shit hole. I will be damned if some easy piece of work whore walked around thinking she was all that by getting my husband to cheat on his wife. I will be damned if she walked out of that relationship with an ego-trip.
It was the best thing I did to fix that issue. It was liberating to send that letter.
Never heard from her again. It has been 7 months since that was sent. And yes he had NC and did not break it with her since D-day other than forced to work with her on a handful of occasions months later.
After that, I never wasted my energy on her again. Chapter closed.