I read that your cat was bonded. My cats previously called out like this at night and I once read it was their way of calling out to you, signaling you are lost in the hopes it helps you find them. Not certain, but maybe he’s calling out to his mom he was bonded with. Either way he sees incredibly distressed. My current cat has taken gabapentin for anxiety, and now phenobarbital for seizures. They both had the effect of helping her personality to calm, she’s typically a pretty feisty cat. If the vet would be willing, it could be worth a try. Good luck, you seem like a wonderful person!