Dude, it really sucks what you're going through...we had to put my cat down not too long ago because of kidney failure.
...But, I needed to be there for him. I loved that cat more than anybody in the house, and...you never know if time passes by that you weren't there to see him to the other side, y'know?
Be there for him, because in his final moments, he's going to be scared...he's going to feel pain for the last time, and you need to be brave enough, that despite it all, you're still there him.
....or her, if it's a feline...lol