Oooooooohhhhh... Shining... I'm so sorry. My heart sank when I read your post. It is so difficult... I am sorry. I know that feeling, like your chest is caving in, like it is hard to get a good breath because your chest is so tight. I felt that when I read this.
To be honest, "Now what?" Well I don't have the answer for that. Whatever happens, just know that you will be ok. Remember, it is just a piece of paper. The feelings he feels and you feel do not change because you have simply signed a paper.
I don't know if this will help, but I just got to a place where I just thought that I would just let him go. He would get the d and then maybe he would see that feelings don't change. I thought that, in a way, it would be OK, because he would feel that with the legal "ties" done, he would feel like the pressure was off, but realize that his feelings were no different. That helped me to accept the process. I felt that if I did that and he came back, it was because he wanted to.
OK, now, I am not trying to compare our sitches NOR say yours will turn out like mine (at all).... however, I shared that because it just helped me get through the process mentally.
I don't mean to rush to that and say this is what is going to happen; things could change any time. But, emotionally, I think you are so strong and that you will be fine.
He is a fool. No doubt about it.
As for what to do now, I'm sorry I can't help, and I'm sure no one would want MY help in that sitch!!!! I am sure someone much wiser than me will be by soon with words of wisdom. Just like they seem to do around here (thank goodness!).