Cannot handle this living in the in between.

My old lady is 16.5. In the last few months we've had a rough go, diagnosed with diabetes but then a second opinion walked back that diagnosis so have been monitoring her pee and keeping an eye on her and she's just not been herself. Not really eating (although asking for food), not as cuddly and just not quite settled. Ended up at the emergency vet just over a week ago for blood in her urine but the tests (urine, blood, cultures, ultrasound and xrays) showed nothing. Today I find she's peed just outside her litter box which she NEVER does.

I am having a very hard time living with this constant worry and not knowing what's wrong. I try to feed her multiple times a day and she doesn't really eat, I check on her when she is sleeping and watch her when she is walking around to see if she's in pain.

The weird thing is that most of the time she seems somewhat fine, and her bloodwork actually looks good. But this stress and anticipatory grief is killing me. If I knew something was seriously wrong I could let her go. I'd be so sad but I could do it. But this in between is so hard and I feel it's just an inevitable slow decline. With a lot of vet bills.

Anyone else been through this? How did you handle it? Thank you.