I appreciate you are coming from a place of pain and won’t like any answer I can give you, so I’ll just respond straight.
I simply didn’t think about it very much. I was obviously in a lot of emotional turmoil, and very consumed with how I felt about my ex-H, my marriage, what was happening with DH, what it all meant for the future etc. I’ve written upthread about what my marriage was like at that point, and I think the reality is I didn’t care whether I hurt ex-H, and was made yet more furious by him not even noticing I was spending hours a night messaging, going out late, randomly having nights away etc.
Even at the time, I did feel more guilty about his ex-W. I dealt with that basically by making it his (DH’s) problem. “I’ll worry about my marriage, you worry about yours” sort of thing.
I do generally think feeling guilty over something you can’t change is a waste of time, unless it spurs you into behaving differently. I don’t think I’ll have an affair again, for many, many reasons, but one is a better understanding of both the slippery slope and the damage a full blown affair causes to everyone involved. I do feel bad about the pain we caused ex-W. I also believe it’s up to her to process what happened and move on with her life. I hope she’s happy. If she’s not, that’s up to her to work on.
I did have many years of therapy where we picked over the bones of both my marriage and affair until there was really nothing more to discuss and I could make peace with it being part of my past, and move on. Someone upthread said I seemed to have all the answers. That’s because most of the questions I’ve already asked myself, and thought about at some length.