I understand the bit about not wanting to let him just drift away peacefully. And you shouldn't necessarily.
But here's a thought. He probably wants the D to go through quickly. What's best for you is to get what you want in the settlement and for things not to drag on and cost more money.
So, use this as leverage. They tend to be more willing to give what you want and not fight about it at the beginning, especially if they are in a big hurry to be D'd and legitimize the relationship with the OP. Take advantage of that. Treat this like a business transaction - you want to get the most favorable terms for yourself, and minimize conflict.
I know the emotional side wants it to be painful for him. But trust me - it's much better to forego that and get a good settlement instead if you possibly can.
Believe me - he'll bring about his own pain just by being himself.