I think you are struggling with the wedding because it shows how misplaced his loyalties and priorities are. Also anything that H does that affects MY kids hurts me more than anything he does to me. That night that I asked him to leave I couldn't live with myself not because I would miss him, but because I would not be the person that allowed him to hurt our kids. Your H's behaviour has impacted on your family, don't you think that could be the reason why this wedding bothers you? In a way other women threaten your relationship with H, but this surrogate daughter being a priority hurts your grandkids. That's how I see it, sorry if I'm miles out.
As job said, you need to let go of that (as well as everything else you've already let go off). Maybe even see it as mildly positive in the sense that it means he might be coming out of his fog?
"There's nothing sadder than a conman conning himself"
“There is freedom waiting for you, On the breezes of the sky, And you ask "What if I fall?" Oh but my darling, What if you fly?”
