Is it bleeding?
which foot is it on?
These things happen all the time! That is quite painful, hence why he does not want you to touch. the paw.
If there is any hanging piece of nail try to cut it off.
You can use peroxide for disinfecting but he also needs a dab of neosporen. If he is in a lot of pain put a sock on his leg, taped at the top so he cannot remove it. You can put a piece of cotton, sponge or a pad around the toe under the sock to cushion it.It can take a few days to grow out, but it will.
If he is really uncomfortable, even a groomer will be able to clip the rest of the nail off.
He may have either benedryl at 2 mg per lb or aspirin at 5 mg per lb of his weight - not both.
Please let me know how he is feeling. I will always be here to help.
I hope your boy feels better very soon.
Sincerest best wishes,