I wonder if there will ever be a reason that will take into account what I did to her?
Yes. You did not take her into account. She was not a part of your "relationship" with her husband. He was not her husband at all in your mind. He was your solution without having to make any tough painful choices.
My ex friend was a sister to me. That love and affection was real. She was there for me for many dark days as a child. She was kind and caring and loving the 20 years she knew me right up until she fucked my ex and had their child. Then she lied every day to my face.
Why? Because I wasn't taken into account as she was searching for her "solution" to a PTSD husband that wasn't a prince to begin with and two (at the time) little ones that demanded her attention.
Why are either of you expecting the answer to justify the destruction? It won't. I don't give a fuck how creative you are you won't every justify that choice, so stop.
Find the thought processes and patterns that didn't stop, support, offer other choices and evict those suckers. That's where your focus needs to be.
Simple answer. "It doesn't". Me: 37
'til the roof comes off. 'til the lights go out. 'til my legs give out, can't shut my mouth