Hi OP. I mentioned up-thread it had happened to me.
After reading your message and replying, it triggered me (which I knew it would). DH asked if I was ok and I cried a little. He comforted me and we talked honestly again and then we went back to our evening. This is 8 years on.... As you can tell, it's been a long road.
We were both newly married when it happened and we'd been together for 8 years previously, since meeting at uni. At the time we were childless, didn't own a property and we earned a similar salary. Both in our late 20s and could have easily walked away.
For me, my husband and I are best friends. I would have been punishing myself by walking away from a relationship I was happy in and wanted for the rest of my life.
His actions since the event have obviouslyhelped:open, honest, apologetic, loving, remorseful etc.
The recovery isn't linear and as you can tell, I'm still hurt.
The good massively outweighs the bad and I am happy with my decision to stay.
We have a wonderful family life and open, honest communication.
Also, I think having options has helped me. I could still walk away if I wanted to but I don't because I enjoy my life and like and love my husband.
Please do what is right for you! 