Hello, I'm Dr. Deb and will do my best to help you today.
This is a really difficult situation with Fritz, isn't it? It sounds as if there may be multiple issues going on with him, unfortunately, which is often the case when our beloved pets start to age.
I'm concerned that his diabetes may not be well controlled if he's now drinking more water but it's also possible that he's starting to develop issues with his kidneys or liver or even his adrenal glands (Cushing's Disease). It's also possible that he's getting a urinary tract infection which is always a concern with diabetic dogs which might explain his thirst and inappropriate urinating. Just because our pets have one problem doesn't mean that they can have more.
I also wouldn't be surprised if he doesn't have Cognitive Dysfunction (CD) issues as well if he's showing signs of Sundown Syndrome (similar to humans where they seem more distressed in the evening/nighttime). These dogs will often "forget" that they're housebroken, they can act confused at times, pant, pace and wander although not every patient will present with the same symptoms. If you think this might be contributing to his issues, please let me know since I do have a fairly long list of supplements and drug options which could be considered for him.
But, to address your question about whether or not it may be time to let him go....This is always a difficult topic and there isn't always a clear cut answer to this question in every case, unfortunately.
For me, it comes down to quality of life issues; this is the priority although often this is very subjective between individuals.
When contemplating this decision, I ask my owners to consider the following questions and will ask you to do the same:
1. Does Fritz have more good days than bad ones? Sometimes it helps to keep track of them on the calendar.
2. Does he still enjoy doing the things he used to enjoy doing (even if for shorter periods of time) or is he too painful, tired or weak or confused to do so?
3. What is his attitude like? Is he lethargic/depressed or upbeat and enjoying interaction with you and your family?
I find that if you can answer these questions honestly and objectively, then it often helps make this difficult decision.
My personal opinion is that it's best to let our pets go before they deteriorate too far, while there's still some dignity to their lives but this is only my personal opinion. For me, quality of life trumps quantity. It sounds as if that was your approach with Benji so I think you know what I mean.
I hope this helps to bring some perspective to his situation. Deb