i understand how you feel now. Your are shouldering the resposibilities to look after your father in law. you r worried that if anythg happen to him, you'l be blamed.
Your situation reminded me of my dear husband's granny. When she was sick, my mother in law was in your position & whole day grumbbling about looking after the then sickly granny until the day the granny passed away.
Frankly speaking, if i'm in your position i dont think i can cope like you. you r already doing your best to help but you need support fm other family members esp your dear husband. My mother in law who is of older generation also have this grievances not to mention you.
When the granny was sick, my dear husband also did not spend much time with her. He is very remorseful for not visiting her more when she was alive. But human always make this mistake "Treasure only when something is gone"
you can vent our your frustrations here but you need to have a good talk with your dear husband. you need a break before you breakdown. Good luck