After having the experience of saying good bye to numerous dogs over decades, it is never easy and doesn't get easier with each experience. Be with him now as much as possible. You choose the time. Prior to appointment day and time give him a favorite food, (we cook steak), lots of love and hugs, talk to him, say thank you, he knows your sad and can feel your energy, so go ahead and cry but include tears of gratitude. If you have other pets, let them be part of this process. Let yourself grieve. When we love so much, it's difficult to make the tough decisions, but you must do what is right for Buster. You are not putting him down, you are setting him pain free - to leap over that Rainbow of Eternal Joy. May God bless you and angels protect you through this journey.
For you and others interested - as an aside - we discovered Nature's Pet Loss, Brooksville, FL who performs aquamation. An all natural process of cremation in water, no hot furnaces or ashes co mingled with other dogs. Only your pet, your pet's ashes, very gentle and loving. They are incredible. They have a small chapel, for lack of a better description, a quiet place to spend time with your pet to say goodbye, other pets are welcome so they can be there for the moment of removal. We have used their services on too many occasions.