Sorry, I thought you were looking for my thoughts on how you could know when it is time to euthanize your pet. After all, after living with him for more than 16 years, it is a very personal decision that only you can make. We certainly can look at the specifics:
The things you listed that particularly indicate a poor quality of life are:
1. Being disoriented
2. Seeking seclusion
3. Avoiding his normal routine of being with you
4. Your summary comment that he is not enjoying life
5. Fecal incontinence
Seeking dark places can indicate pain---especially eye
pain. If Scruffy has been dealing with kidney failure for a long time, he may very likely have blood pressure issues. This can cause ocular issues and headache.
When treatment for kidney failure is not going well, it tends to cause severe gastro-intestinal signs. Dogs will suffer from poor appetite, vomiting, and weight loss. If Scruffy is experiencing those symptoms, they will certainly decrease his quality of life. You can try to minimize these symptoms with medications like cimetidine and amphogel. We have to accept, though, that at some point we will no longer be able to relieve those symptoms. If his appetite is consistently poor and he is losing weight, he is most certainly suffering.
Specifically, what questions can I address for you and Scruffy?
Or would you like for me to OPT OUT so another veterinarian can assist you?