My heart hurts for that poor dog. He is one of the many reasons I have stayed as long as I have. My AH brought him into our marriage. He is a rescue dog, who was very badly abused by a prior owner. He is definitely in the twilight of his life, and I will miss him fiercely. I refuse, however, to be guilt-tripped into feeling responsible for my AH's lack of money for his surgery. AH spends hundreds of dollars a month on beer, tobacco, hanging out in bars, etc.
Thanks everyone for the input. My concern that AH will drink and drive with our son is very low at this point, but I am also very aware that the drinking is almost certainly going to escalate quickly as I move out and file for divorce. I'm not willing to take the chance that AH will make a profoundly stupid decision with our son...you all are absolutely right.