OP, whether you can see it or not right now, you are following a script. In years to come you will curl up with embarrassment at the memory of all this. It is not a pleasant feeling when the scales fall from your eyes too late and you see things for how they really were. It is an awful feeling to judge your own behaviour and find it so lacking.
It doesn't matter if you truly love him or not, with regard to how this will affect you long term. You will still feel sick when you remember things you did and said.
So if you can't stop this for your partner or for the thought of OM's wife, then stop it for your future self.
I had an EA and felt that I was in love. I was single, he was married. He didn't pretend that things were dull at home. He said he loved his wife and didn't understand why he had these other feelings.
I let the situation and my feelings go way too far. I didn't have the foresight to see that the pain caused would be so far reaching. I was caught up in my immediate feelings. I was weak. And all the drama meant I was feeling something - not just plodding along being a bit lonely.
After a few weeks of intense emotion, we went no contact. It was torment. And I had no one to blame but myself. But I was still in this bubble of drama and emotion. Then I had an email from his wife. She had known something wasn't right. She had found out about me. Her message was amazingly measured and dignified. She just wanted to make sure I would stay away. I promised her I would. After that it was easy to keep up the no contact. Once I had made the promise to her it was like an extra lock on the door if ever I felt weak.
I felt utterly ashamed. I still felt heartbroken. I felt unable to confide in my friends. There was no relief and it was all my own doing, which made it feel even worse.
I did a lot of reading on mumsnet. I read about the effect of affairs. I read about why people give themselves permission to have affairs. It helped.
Whenever I thought of him - and he still comes to mind now and then - I made myself think of how I felt when I read his wife's email, and how I would feel if I met her face to face. Small and stupid and ashamed.
This is a selfish thing you are doing, but I think you know that. Telling you to think of others isn't working. So think of how you will feel when it comes out and you have to explain to your partner or to OM's wife. Protect your future self from feeling sick to the stomach forever because of something you do now.
Only you can know the truth about your relation with your partner. But from the outside it sounds as if you don't love him and have no respect for him. Are you scared of being alone?
Come on, OP, what do you think is the right thing to do? What do your own morals and upbringing tell you?