Hi OP,
I am worried about you because your messages have sounded increasingly despondent. You have mentioned before that you are in recovery from addiction (well done you, that is a really difficult thing to do) and that you have a condition where your skin is easily damaged. You are clearly a kind, compassionate, caring person who has spent a huge amount of time, effort and money trying to get Pod to settle into his new home.
Please think about your own health and wellbeing here. It sounds as if Pod’s presence is negatively affecting your health, your recovery, your mental wellbeing, your relationship with your neighbours, and perhaps even your job and your relationship with your partner.
It may be that through many more months or years of hard work and sacrifice, you would be able to get him to settle into being a pet. Other people comparing him with their pets cannot know that Pod is the same because they haven’t met him or you, and may inadvertently be making you feel that you must keep trying because they did and it worked for them. There are no guarantees that anything will work for you and Pod. Some dogs, like some people, just have genetics which make them unable to fit in socially. As a hunting dog, he will have been bred from hundreds or thousands of generations of dogs bred to live in kennels, obsessively hunt prey and not interact with people very much. Some settle into homes eventually, but not all.
I think you should have a serious discussion with your partner about whether the cost of keeping Pod (and I don’t mean financial) is too great. If it is, try not to feel a failure because no-one could have done more for him than you have. And as I say, he is bred from dogs used to spending the majority of their life in a kennel situation so returning him to the charity kennels is totally ok.
When having your discussion, be really honest about whether you are going to be able to stay well if he stays. If you become unwell, you are not going to be able to look after him because you will need to spend all your energy looking after yourself. That would not be a good outcome.
Of course only you can make this decision. Clearly you are grieving for your grandparent and that will be making things worse. But it doesn’t sound as if this is a decision that can be delayed.
My qualifications for this advice? I’m a veterinarian (retired earlier this year) who also has a Masters in human mental health.
Good luck OP and I’m sure I speak for everyone when I say I so admire your dedication and hard work with Pod. But now you need to put your own health and wellbeing first (placing your oxygen mask first).
Very best wishes, you are amazing.