I suppose that is my point. Do what you do for you, not trying to control the situation. We didn't break them, we can't fix them and the only person we have control of is ourselves. (i.e You are not his mother to give him permission to do *whatever*, if you see what I mean.) Letting him go, that is for you. You can't control him, anyway, so better to leave him to his MLC and take care of yourself and your kids. Sure, be kind, pave the way. Treat him as feels right to you. If you only do what you need for yourself and your kids, with no thought of how it will affect your MLCer, you won't have to second guess anything because you are being true to yourself. For myself, I never told my MLCer I set him free or really anything. I just left him to his own devices, since he didn't care a whit for my feelings anyway. Your mileage may vary.
Him saying he's given it his all it script, you know that. No spark, script. No way forward, script. In his mind, there is something external out there (OW at the moment) that is going to make him HAPPY! He doesn't realize that true happiness comes from within.
Your sister will not understand. She will likely think you should "just move on". It took a while for me to get my family to understand that I was going to hold on until (I didn't know "until" what at the time, but I was going to stand until I couldn't any longer). My until happens to be when the Divorce finally comes through (if ever), and my family was thrilled when they discovered I at leave had a time frame.They only want what they think is best for me, but they don't understand.
I can understand the anniversary of his father's death being a trigger for his mom. It may well be a trigger for him, too, and he is projecting his own upset by being worried about his mom. It's a way to avoid his own feelings.
Yes, this is very tough. One minute at a time, one hour at a time, one day at a time. I look at the folder on my computer I created for all the documents I knew I'd have when I started all this, and I still remember the pain and sorrow from when I created it. But 3 years later, I don't feel it so much anymore. Three years seemed like an eternity back then. It does get easier.