Hope your dog is okay or doing better after the vet treatment. It must be nice to at least have their companionship through this hardship.
Yes, it's hard to understand it all. I came a across a couple of "old" cards (1 year ago or less) that were somewhat similar in message.
I hope he is able to reconnect and see what he has been missing with you, and the potential for things to be great for both of you. It seems like he is in another world at this moment, so that means you need to be good with yourself and build the most tolerable situation you can in the midst of some difficult holding of space.
