I remember you and your sitch. I never posted anything to you, but I found insight into my own sitch thanks to the posts you and your XH made.
My XW probably regrets the hurt she gave me and has come close to saying as much, but I think at the time she saw no other alternatives so sacrificed our friendship and M to her career and OM. As time has continued to pass, she keeps making overtures about being friends and wanting to stay involved in my life, sometimes even coming close to expressing regret, but I feel like I've had to harden my heart against her so have stayed distant. No one I've ever known or been friends with would have treated me the way she did. Like DDay mentions, I still love her, but I will never look to her for friendship. I say this so you know where I'm coming from - I can't say it's a good reaction or bad reaction, but it is my reaction. In any case, I'm sure your XH has hardened his heart as well and would probably not be all that receptive to an apology, or at least, it probably wouldn't be as meaningful to him as it would be for you.
That said, apologies are more for the person who gives them. So if it would help you find closure, why not write the apology you want to? It is up to the receiver of an apology to either respond with forgiveness or hold on to bitterness, but you would at least have the good conscience of admitting your mistakes and leaving them in the past.
I remember 2 other posters that struggled with similar issues. They aren't exactly the same, but maybe you can find something useful. Here are links to their posts:
