Setting Boundaries for MLC Alien H

[In Limbo]

H was not able to get in to see the MC today. But things are coming to a head. He has started R talk and a lot of things that he blames me for and resents me for are coming out. I'm not sure how to respond other than to validate and apologize for those things I believe I should apologize for. He says he feels like I emotionally abandoned him years ago. Our problems go back to when S11 was born and I put children before H and M. I cannot change the past. I was only part of the problem, H contributed as well but I had told him I was willing to move past the past and I mean it. I'm ready to forgive all the past problems if we can just move forward and deal with the issues - get to the root of it and fix it. He is skeptical of all the changes I have made and said "after all these years that you haven't been here for me, you suddenly make all these changes and expect me to be here, to want to work on the M?" How do I respond to that? So far I've just said that I can understand how he would feel that way and maybe it doesn't seem reasonable. I told him that I do want to be married, to him, but not the same marriage we've had. Truth is, he'd have to make changes too but we haven't discussed that. I also told him that if he needs to go, to just go. I'm thinking maybe he needs to be totally separate from me for a while to figure out what he really wants and to see if my changes stick.

He's gone to dance class and said we'd talk when he got home. How do I DB through this R talk? Is this when I should be honest and open or should I just validate? Help?!?!