How to give loving care to someone who doesn't appreciate it?

Oh, dear. I have lived with my fiancee for over two years in this situation. Somehow, I don't know how, I found myself taking over the role of caretaker. I don't even know quite how it became that way. He was well, we all lived together, it was a joy to bring him elaborate home cooked meals, please him, live my life with the love of my life, etc.
Then something will happen with my FIL's health. He won't listen to us, had horrible bouts of insomnia which led to falls, which led to long, extended periods of recovery where he would give us a daily, constant rundown of every ache and pain. EVERY sensation (example: oh, this feel strange on my tongue, oh, I don't like feeling heat on my body. We remove a blanket, then he complains because his legs are cold, and on and on.)
After a number of years of this, I begin to dread when he awakens because it invariably begins with complaints of the smallest things, a nasty, sort of bitter attitude, and then I find myself bringing him juice and fiancee making cereal and bringing it to him while he complains that there is either not enough or too much milk in the bowl.
The most hurtful thing is that he finds fault with almost every meal he is served in his chair. I would give anything to be able to lounge in a chair and have drinks, meals, snacks served and empty plates removed like he enjoys. Everything is a complaint.
"Too salty". "Too much". "WHAT is this?!".
You try to be nice, ask if he wants some dessert, and receive a curt, "I don't know. What do you have?"

AAAAAAHHHHHHHH. Oh, my goodness. The joy of care-taking is completely gone now. If we borrow a couple of sections of the Sunday paper and present him with the rest he barks, "This must be the SLIM edition."

If we leave for a few hours to see to my SO's previous son's karate belt test and come back after having told his father explicitly where we are going, why and how long, he attacks us by asking, "WHERE WERE YOU?". "WHY DID IT TAKE SO LONG?"

I see so many of his dishes that are barely touched because he found something wrong with EVERYTHING. He claims he is unable to get his own drinks, including water at the sink, yet will readily raid the fridge and eat family ice-cream with a spoon straight out of the carton. I see him standing, hunched over in front of the TV, wolfing it down. But he can't get his own juice or water?
I have begun to hate serving him. He doesn't like anything anymore, finds fault with everything that is made by me with loving intentions and never, ever thanks or acknowledges the hours I spent in the kitchen to make a nice meal for him. It hurts.
Everything in our house now seems to revolve around his daily issues. When my husband was gone he approached me about picking his nose for him and cleaning it out so he could have better oxygen intake.
He just got fitted for a partial denture and hates it, even though it is a HUGE improvement (trust me). He claims that he can't put it in, doesn't like the fact that it might have to be cleaned and now wants us to put his teeth in for him every morning.
AAAAHHHHHHHH. NO.
In a moment of admitted frustration, I did tell my SO that I resented feeling like a Denny's server and that I dislike very much the very personal requests he specifically asks of me (picking his nose for him). I told SO that I feel the next step is being asked to wipe his dad's ass, and I feel bad for that, but I have, over the course of SOOOOOO long, been asked to do the most awful things and I don't understand why this is my responsibility. He is not my father. I faithfully and lovingly did things for years. We are in a position where we need much more space and privacy.
His dad is very catty and sarcastic now, lots and lots of bitterness. Not a nice man where he used to be an absolute angel. Sorry, but he used up my pity when he began to abuse me verbally.
I have asked him to think about hiring a personal caregiver to produce satisfactory meals for him and refill his drinks all of the time so he can sit in his chair. He looked at me like he was crazy and said, "Why? You are here."
Ummmmm....did I mention I have an infant and SO has an autistic son we watch over and care for during his visitation? I am sort of full up. The fact that he said that makes me feel TOTALLY taken for granted. I now really, really dread SO's father when I once loved him.

For these recent posts about spouses changing because of live-in care or general care taking, this is one thing I hope they consider.

Someone fell in love with you and imagined a life with you. I can't help, at this point, to say that it is VERY unfair to inject a parent into that mix knowing that they are going downhill and there are years of pain ahead for your spouse to deal with that they did NOT sign up for. The vows you take or have yet to take but feel in your heart are related to your spouse. NOT to your spouse's parent.
I wonder when my life will ever begin again. Maybe it won't. I didn't want this to be my new life.