WH, I'm sorry you're going thru this. It's obvious that you don't want it. I wish it could turn around for you, but at least you're taking care of what you need to. A lawyer is a good idea if the D is actually going to happen.
I hope you can lessen some of the animosity you have for your H for making this decision. It will only hurt you in the long run. Can you reflect back to a time before you were M'd, when you were dating other people? Did you ever break up with someone? I'm not suggesting that M is on the same level as dating, but it might give you some insight into what it's like to be in his shoes. Was there ever anyone that you broke up with that didn't want you to? Did breaking up with them make you a horrible person? I don't think so. You probably just evaluated the R and decided it wasn't for you. Can you think of anything the person could have done to make things work out that you would have continued dating them? Could you have stayed with them anyway, just because they didn't want to break up? I think it takes two to make a R. Insisting that someone stay with you when they don't want to doesn't qualify it as being a healthy R. Again, not at all on the same level, but hopefully something to get you started.
I'm just suggesting this because I saw the animosity that my H carried for his ex-W, and it impacted him and their R and his R with his kids -- and ours! -- for years. If he could have just let it go and focused on the good he had before him, his life would have been so much better. The end of a M is not the end of the world. It's just an opportunity for something different, possibly even better.