OP is upset enough, she clearly already feels awful about this and her poor dog and you're accusing her of thinking of him as an inconvenience? Where is your compassion?
Exactly this ^^.
It is never easy to let a much-loved pet be PTS. Frankly, most of us tend to hang on to them for much longer than we should because we can't bear the thought of letting them go - worse than that, of effectively "murdering" them. We convince ourselves that a dog which is doubly incontinent and dragging it's back legs, or a cat which shows obvious signs of dementia, is still having"quality of life"
Often we are wrong. The obvious signs are frequently less dreadful than the symptoms we cannot see: multiple organ failure, anxiety (often sheer terror at times), distress at losing control of their bladder and bowels.
Animals, much as we love them, aren't people. They fear pain, not death as they have no real concept of what may or may not be waiting for them in an afterlife.
I think that the very fact that this dog has reached the grand old age of 17 shows that he has been loved and cared for throughout his life. Things will NOT get better. He will become increasingly physically and probably neurologically ill, and increasingly distressed, especially if OP is forced to segregate him from the rest of the family. He won't know why he is suddenly confined to the kitchen when he was previously in the living room with the family.
He is 17. He is ready to go. Even if OP doesn't smack or shout (and I'm sure she doesn't), he will pick up on her frustration and it will upset him. OP has nothing to condemn herself for - I think she knows herself that the time has come for him to be PTS. She doesn't want to do it, and I think has probably hoped that someone here could offer a viable alternative - instead she has been subjected to abuse about "getting rid because he is now an inconvenience." Some people on here have been very cruel.
OP - only you can make this call, but what I will say is that if you decide to let him go, you have nothing to reproach yourself with. He has had a long and happy life in a home where he is much-loved. He will be tired, his life will be increasingly a burden to him, and to gently let him fall asleep in your arms (either inches own home or at the vet's) is really the kindest thing to do for him.
Yes - you can probably keep him going for another year or two, but at hat cost - to him as well as you? Increasing pain, increasing distress, decreasing mobility.
For those who say "would you kill your grannie if you got the chance?" - well, frankly, if my grannie was in so much pain, or mental distress, that her life wasn't worth living, then if it were legal, yes I would. A gentle release from care and pain is something that we can offer our pets that we can't have for our relatives or ourselves.
OP - whatever you decide, you have the support of many people here. 
It is not an easy decision.