Why do I keep trying?

Eighteen months ago my WH met someone and started an affair. I found out a year ago. He accidentally sent me a screen shot as a message from her came through so I saw her message. I was away from home with our daughter and his family and I called him and made him come and get me then spent a week trying to find out the truth. He told me that he had met up with her twice and they had slept together that they were messaging occasionally and that was all. He said it was over and he wanted to be with me. She was a random she lives miles away and he said she was an ego boost he didn’t find her particularly attractive but she made it clear she wanted him. We were not in a good place. I was grieving the loss of my father and grandmother and our relationship was already rocky. I was devastated completely broken. I chose to stay and work things out. Firstly hysterical bonding? WTF is that about? We had more sex in those first few months than I have ever had, I lost my mind. We had threesome sessions with escorts (at my request and he wasn’t allowed to have sex with her), we did things in the cinema, the car as he was driving, went to sex shows. It was completely crazy. One year on and I felt like I didn’t have the full story, I went digging through his devices and found other hotel reservations and messages. All from the same time nothing new but it feels new to me. I feel like the last year has been wiped out and I’m back to the feelings I had a year ago. A year of building trust, healing myself all smashed to pieces. He has been since day one accepting of all responsibility he is ashamed and he has been trying to make things better within our relationship (I have not really, I have been trying to survive). He doesn’t understand why this is so difficult for me. He sees it as not good because he lied still but as far as he is concerned I am acting like he had another affair and he didn’t. He wants us to go back to counselling, to try again. I already tried, I don’t know if I have the strength to try again. I don’t know if I am able to fall in love with him again (I love him he is father to my children and there is a lot of history here - we’ve known each other 30 years been together 20 but I currently despise him). I don’t understand why I can’t just walk away, why I’m still contemplating trying to find something to salvage.