7yo domestic shorthair having behaviour issues since our dog passed away.

I have a 7yo domestic shorthair, we put our dog down about a year ago due to cancer. Ever since, he’s been really clingy, meowing a lot, pacing, urine marking.. I took him to the vet, as he has a history of bladder crystals (which are now gone thanks to a prescription food). The vet said his health is good, he has no bladder crystals, however there is blood in his urine. The vet suggests it’s due to stress (ruled out infection etc) and diagnosed him with a condition called feline idiopathic cystitis. She suggested we try FeliWay, which I purchased and set up in my home a few days ago. I told the vet about how drastically my kitty’s behaviour has changed since our dog passed away. The vet said I’m projecting my own grief about the dogs passing onto my cat.

I understand where the vet is coming from, but everyone in my home has noticed the change in the cat since then. His personality changed, he used to be pretty aloof and independent and now he’s clingy, gets separation anxiety.. am I crazy?? Is this due to the dogs passing? They play fought a lot, I never would’ve thought they were THAT close. The only reason I haven’t gotten another dog is because of finances. Any thoughts or suggestions are welcomed.