As always I follow you and your sitch ... and as usual everyone is spot on with thier comments
Just wanted to share ... for a moment lets put what your H and HWW have done aside ... looking at this from a detached perspective, not where that hurt and pain still resides.
Your H is trying to work on some sort of r with your D, granted D might be Lil-Mighty ... she is lashing out with that same pain and frustration I think you might feel is just you, well H devastated more than just Mighty, S and D also are dealing with the abandonment and dealing with it and him in their own way ... to me D is going about it as you would .... not your circus not your monkeys ... that's H's issue, its one hell of a bridge dude will have to try to rebuild if he truly wants to be in her life at any level.
^^^That being said ... and where is is ... typical and MUCH easier to say its all your fault than to truly own up to what he did. Facts are facts, feelings are feelings ... on paper ... dude up and left his family to run off with another woman, had a small window of opportunity there but still chose door #3 ... that's on him Mighty ... HIS choice, I know hww is a manipulator but the end of the day if H is going to drink poison ... he drinks the poison ... again ... his choice, his crisis, his $hitshow to live in.
I can only tell you that I feel for you and all you have been through, the pain and hurt is not fair ... no one person should have been put through what you have had to go through ... however for your kids ... stop giving your H and hww the power, take those reigns and enjoy that graduation, its a HUGE deal and you are there .. the rock .. celebrate the fact you get to be there for S and shed a happy tear as he is moving onto the next chapter in his life