Audrey: anybody who had to make that decision about a beloved pet, including myself, knows how you feel. But it comes a time when, because we love them so much, we have to let them go to a place were there's no more pain and suffering. One day we will see them again at the other end of Rainbow Bridge.Don't be afraid of crying in front of the vet, he will understand and, as Souraya said, he probably also cried when he had to let his own dog go.
Whatever you decide, we'll be thinking of you and sharing your grief.