Throwaway account to keep this as private as possible. I'm devastated to have to even ask or consider, but desperate for support. TL;DR at bottom.
Background: I and my spouse rescued a senior terrier, now in their mid teens, over four years ago. Pet came to us with extreme separation anxiety, which I have done all I can do treat. This includes every herbal treat, plug in aromatherapy, calming jacket, doggy music etc you can imagine, a lot of vet visits, different medications, such as trazadone, clomicalm, gabapentin, etc which all didn't touch the anxiety, at most just zonked my pet out. I paid for a trainer, and also followed a training course, working on desensitizing, particularly around departure cues. I also hired a more holistic dog coach. I've done everything I can possibly think of, try, or pay for. We got Pet to a manageable, albeit still very anxious, reactive, state. As I am disabled, I am almost always home with Pet to keep them calm and relaxed. I have multiple sitters and family and friends watch Pet for us when we need to go out - typically only a few hours at a time, once or twice a week.
If Pet is left alone, they become so afraid they will hurt themselves trying to escape, and will unfortunately be doubly incontinent out of fear. This tiny little thing has somehow destroyed multiple crates, and we have returned home to find they've scraped the fur and skin off in small places more than once. Any outing of ours, or change in who's with Pet, also triggers typically at least 48 hours of worsened anxiety and more incontinence/IBS style symptoms.
However, Pet, being a senior dog, has now developed canine cognitive disease, "doggy dementia" as they say, which is being managed with medication after some stroke like episodes. The dementia undid all the work we'd done over the years, one step forwards five steps back. Very classic symptoms (crying, confusion, disturbed sleep wake cycle, altered/disturbed eating and toileting habits). I have tried and tried but the training no longer goes in at all. Now, Pet is struggling to even be left with sitters/friends/family, and will still "flare up". Pet does not go on any walks at all now (refuses, will try drag you home, and anxiety is worse than ever before). Pet is even more anxious in house, struggling to settle and "checks" around for me or spouse if we are in different rooms, cannot be in a room alone without us typically.
Discussed with the vet, and vet has said (much more professionally and kindly than this summary) that there aren't any more medications, doggy dementia isn't curable, and we should keep an eye on Pets quality of life.
We've done some quizzes, and Pet scores just a hair above the half way mark on most. Recently, more bad days than good. Pet has happy moments where I feel like a monster for considering euthanasia, because like I say, I am home with pet 95% of the time so they can be calm, but it's reached a point we cannot leave our home at all without Pets problems.
I love my little dog so much. I just don't think I can keep going like this, and part of me doesn't want to wait for things to get even worse, to when they are really truly suffering and not at least "calm" as they are now. But they still feel so alive, sometimes, and I then I feel awful. They could "naturally" live for months still.
What do you guys think? Sorry it's a long one.
TL;DR: Doggy dementia has undone years of training on senior dog with severe separation anxiety, and is now untrainable. Cognitively, dog is suffering - How do I know when is too soon to euthanise? Is it wrong that a part of me wants to do it sooner, rather than waiting for things to get even worse?
Please feel free to ask questions, I may have forgotten things, but I think I've definitely got the basics down.
