I feel that there are many ways that we can be "not faithful" to our partners. If it's something that you would not share with your fiance then it's probably not anything that is healthy for you or your relationship. Right from the beginning I felt like my husbands drinking and drinking lifestyle was the same as if he had a lover - it was a part of his world that I could not and would not have any part of. He brought something into our marriage that he loved more than me and because of that, he was not faithful to me. Does that make sense????
As far as the porn goes, I'm sure you know that it is an addiction to some people. I woke up many times in the middle of the night to find my husband watching porn on the TV in the bedroom as he was laying next to me, I won't say that he was addicted - although he has an addictive personality, but it made me feel dirty.
The good news is that you are activly working on your recovery, so don't beat yourself up over all of this - work through it.
Personally I think you should break all contact with that woman, remove the temptation especially because a line has been crossed with her and theres no turning back. Don't create a world that your fiance can't be a part of.
It's apparent that you love your fiance, focus your energy on her.
Your in my thoughts,
God has a plan for me, I trust in God's plan.