You can talk with your vet and agree that if X happens (numbers start to go this way, the pain meds exceed X amount, certain symptoms appear), the vet will see you and end this for Leo's sake. Not doing this under duress is a good thing.
When one of my dogs was having kidney issues and we'd done several IV treatments while increasing pain medications, my youngest daughter looked me in the eye and said, "You have to be the adult and do what's right for the dog, not what you want." The dog stopped eating. I tried to make it look like a regular vet visit when we had her taken into a room, and she passed away. It was tough, but I had to do it for her.
Be strong for Leo.
