Sweetie, I'm sorry about your father in law. I think the best thing you can do is kiss and hug your husband. Sounds like his biggest regret is not "having" a father, and everyone wants their parent to love them, even if they deny it. My dad and older brother didn't have the best relationship....know what my brother told me through tears....(his and mine) all he ever wanted my father to say is that he was proud of him...period. And he never got that. So I suspect your husband mourning the loss of a father that sounds like he didn't have. Some situtations, try as we might, just can't be FIXED....
God bless