"There is no way I could completely understand what you went through, I am sorry. What I saw was the pain and I was, and am, "broken" and devastated I could not do anything to stop it. Call it ego, stubbornness, stupidity and.or anything else does not change the fact of where we are and the relationship, with you and the boys, should have been placed above everything at all times."
The overall apologetic sentiment is OK but ... I would word a couple of things differently.
I wouldn't say "there is no way I could completely understand ..." And I wouldn't volunteer any self-bashing adjectives, and say something about where you're headed. How about:
I am so sorry for what I have done. I am beginning to understand what I have put you through. I am broken and devastated that we are where we are. I should have placed you and the boys above all else long ago. I have been reflecting on who I had become in the last few years, and have been thinking about who I'd like to be. I'm working on setting a new course to make myself a better person, regardless how everything turns out.
Is that too cheesy? I think you were good to leave out any direct pleas for her to reconsider or take you back.
Me: 50, MLC/WW 45 Young kids Nov 2015: BD1 Apr 2016: BD2 Jan 2017: W filed Feb 2017: D final