People put too much emphasis on whether someone can change, when sometimes it is the affair that changes someone.
In my experience someone who has multiple affairs becomes swept along with the pattern of cheating. But someone who has a one off affair in response to an unhappy marriage may regret that affair and never even contemplate doing it again.
I had an affair. Not justified, not OK, but it was the catalyst for me to end an emotionally abusive marriage. If anything, I changed in order to have the affair. And when it was all over, I didn't have to swear I would never do it again, I just knew that I never could.
I didn't leave for OM fwiw, my H would have taken me back in a heartbeat, but I realised that I could never go back.
I have a new partner now who knows my history and trusts me implicitly. The very thought that I would ever become drawn to someone else again just doesn't even feature in my thought process. It's as if that part of my life never happened. It did, and I will forever regret it, wish I'd walked away when I realised things were as crap as they were, but in truth society doesn't support someone's right to end a relationship for anything other than violence or infidelity. Emotional abuse doesn't count, and even when I explained to people what had been going on in my marriage their response was "but he never hit you."
My ex on the other hand is now emotionally abusing his new partner in the same way. He has eroded her freedoms in the same way he did mine, and is gaslighting her into believing that she is all alone in the world and needs no-one else but him, and that the world is in fact against her.
What it comes down to though is taking ownership of the things that you've done, and realising that for some even a one off is a deal-breaker and they wouldn't go there for fear of being the next broken hearted victim. If people don't trust then they won't want to be with someone who has cheated whatever the outcome or regret. And that is something which a cheater has to carry even if they also carry the regret of what they've previously done.