Hi, and welcome. Honestly, it sounds like his issues are both chronic and complicated. You’ve been through a lot and are obviously taking good care of him. I would consider getting a second opinion just to have a new frame of reference, and possibly ask both vets what they think the long term effects of the medications he’s on may be. It may be that he needs to go off some for a while, or there is not lasting damage that would be any worse than living with the chronic problems. I just don’t know, and a vet would. I doubt you want to leave your current vet, but a fresh insight might give you some peace of mind, and a back up option if you ever find you can’t reach your vet and need to take him to someone else.
If he’s grinding his teeth in pain, not pleasure, it does sound like a visit may be called for. Write down your questions and bring them, or even email your vet, or a new vet, and ask them. You will probably need to make an appointment for the discussion, but with your ongoing current vet, she may be able to relieve your concerns on these questions directly via email Worth a try.
(And glad he is enjoying his new companion.) 