I think that having you pet die when you are there is one of the saddest times in a person's life. We love our pets just like we do a family member, and it is often just as heartbreaking to watch them die as it would be to lose someone in your family, or even a close friend.
Sometimes, when a pet is dying, and suffereing, and there is nothing that you can do to ease the suffering, then having the pet put to sleep is the very last kindness that we can do for our beloved pet.
I have had to do this , and I think that if you can at least be there and hold your pet when the vet iss putting them to sleep, then your pet knows that he or he is being held and loved at the last minute of their life.
A few months ago, one of my close friends lost her little Pomeranian that she had owned for many years. Ruthie was just old, and she started having heart problems, and finally she developed some kind of seizures.
My friend was just too broken up to be with her, and since Ruthie also knew me very well, I was the one to go in to the vet's office and hold her while she passed over the Rainbow Bridge.