how old is Zak? I'm thinking around 4-5 since you said in just 4 years.
It's obviously up to you, no one can make the decision for you..he's on ALOTTA meds
I honestly don't know what I would, tho I've had some hefty vet bills, but not continuous issues
I dunno, have you thought of consulting a homeopathic vet and start over??
Very tough decision, he's a gorgeous boy