My heart breaks with you, it is beyond cruel.
All I can say, having done this at home, is forget nutrition, give as little fluid as you can just to get meds in, and tell him you will be ok if he goes, that he does not have to fight this any more. Have you said this out loud to him? Honestly sometimes this makes all the difference. I know I told Chris this about 2 - 3 hours before he passed.
Give him all the meds he needs to stay comfortable - don't let him start becoming uncomfortable or distressed and think you will just hold out a little longer. The moment you see signs of discomfort be ready to give him palliative meds.
You won't 'kill him', but you will help him pass more quickly and in peace if you stick purely to comfort of body and of his spirit.
Inside you are screaming in pain I know, but to be honest he can't go too much longer - just keep the meds up know I'm holding tight to your hand. I so wish I could do more.