Oh my gracious what a horrible thing your little Lovie is going through! I pray to God that he makes it but thankfully as you got him to the vet ASAP, he's probably got a much better chance than he would have had. HGE is just the worst but dogs do make it. He's big, he's strong before he got sick & he's got excellent medical care & we'll all be praying. Try to stay as calm as possible tonight so you won't get sick yourself as once he's home, he'll probably be weak & need mommie to wait on him hand & foot!
Just think if he were a tiny and had virtually nothing to fight this awful thing with but as it is, his sturdy body could be strong enough to withstand the course of this disease & bring him through. Please update, even in the night, if you hear more tonight. You are both in my prayers.