I had a similar incident with my dal. His name was Chief, he bit a friend of mine (2nd person he bit). Both were bad bites. He was a wonderful member of our family. He was loyal and trusted only family members (both extended and immediate).
Unfortunately, I saw no option. I held him until the very end. The vet was fabulous, they let me stay as long as I needed.
It's been 7 yrs. and I still hate it. I miss him & wish he were with me. This was the hardest decision I've ever had to make.
I understand how you must feel.