my sister is a vet nurse and she says often people put their animals through an awful lot because they can't bear to let them go. One girl had spend £3k on her cat and my sister said if she saw how much the cat had to go through between dropping him off and picking him up she would be mortified. my sister tries to be very blunt on the records but the woman doesn't want to hear it. All i can say is, when the end is coming, explore deeply and honestly with the vet what the animal is going to go through and do your best for the animal not for yourself. Give them a good life and then go with them on the difficult journey and don't delay that journey because it hurts, when you know deep down it is inevitable.
Sometmes i don't think vets are completely up front and they will keep giving you alternatives which they know don't really work. i think this is because they are duty bound to do this. However, ask the question. Ask them if this is the best thing for your animal. This is what i do, and often the look on their face says it all. Both me and my vet agree that just because you can doesn't always mean you should. She knows i expect her to do the best for my pets even if that hurts me. And yes it hurts to face it, but i always say that those people it hurts the most are the ones who have done their best by their pet, because the more you invest the harder it is to part. it's the price we pay for the investment and love we give unfortunately, so you should never feel guilty. Feel the love, and feel the loss, but don't feel guilty.