I can’t take it anymore.

OMG Maggie - I SO hear you!  Different issues on my side (no pain med issues), but everything else, spot on.  I am into year 3 of my sentence.  My FIL does not like me any more than I like him. 

I have been "round and round" the "where are we going from here talk"....  My husband (only child) and I have fought more this past 3 years than our entire marriage.  Sounds like you are at the same frustrating, impasse as well.
I don't know what your or FIL's financial situation is.  Would it be possible to add on or find a way to separate some of the living quarters?  Like you, my room is my only space and I RESENT the hell out of it.  I am Blessed to work from home, however, that puts me just on the other side of the door from my snoring, smelly FIL ALL day. 
Not to be negative, but you really need to understand that these feelings will not just disappear, unresolved resentment festers and boy when it blows it blows, trust me. 
Here are a couple of things I have had to do that may be of help to you.
1)  Tell your husband that you need to sit down, privately, uninterrupted and lay it on the table.  He married YOU, and while sometimes a parent does not even deserve the care that is given to them, it does not mean that the "child" should dump the family they made a willing commitment to, in order to get and fetch for a parent.  In the best cases, both child and spouse willingly work together on this type of care; HOWEVER, your life, needs and happiness should never be put to the side, indefinitely, to do so. 
2)  Set timelines, even if they have to be adjusted.  One of my biggest mistakes was not setting expectations and timelines.  This is a must....  if not, you will feel like you are dangling out there, with no hope and no power. 
3)  I hope I am never in this position myself, but I think it is so unfair for parents to put the "don't put me in a home guilt trip" on their kids.  While no one wants to be dumped off and forgotten, you really need to take stock of what you are asking others to do, and the impact on their lives.  Selfish I say.
4)  If it is financially possible, go away together, and work on restoring your relationship.  In home care costs, I know, but I feel that my FIL's funds can be used to cover the in home cost of care for us to get away.  A lot cheaper than him being in a home.  If you get sucked in the endless vacuum of your life orbiting around him, I promise you will lose yourself, and possibly your marriage
5)  While it was almost unbearable for me to have the frank discussion with my husband, I had to do it.  Meaning, if we do not make a workable plan, build some separate living or something, I'm out.  I have been married 31 years and would have never guessed that this would / could be the thing to break my marriage.  My grown children are mortified to think about how this impacts our marriage and frankly they resent their grandfather for his past "skirt chasing" lack of planning ways.

I am SO passionate about this because I had absolutely no idea what we were getting ourselves in to.
My hope and Prayer for you is that you will be "heard".  Do not beat around the bush - say what you need and have to have.  Be prepared to "take a break" if needed and go your own way for a while.  I truly hope your husband will not let this happen and will open his eyes to what is going on.  I have told my husband 100 times that there would be no way in hell he would put up with my family sucking all of the joy out of our world - that would not last 2 weeks with him, so why am I any different? 
You need Joy and happiness back in your home "YOUR" home.....
Please keep us posted.

Oh my, that is a tough one.  Personally, I'd decide where I would move to, and how to support self, then tell DH how desperately upset you are.  He needs to move Dad, or you will need a separation.  One of you would need to move.  A time period for moves would need to be allowed, but not open ended. 

Another possibility is to take a vacation, so DH does all the caregiving. 

Whatever discussions and decisions, yes it is normal.  It is ok to own your feelings, and it is ok to say enough!  I can't do this anymore.  I truly wish you luck.

Your husband needs to man up and honor his vows to you.

Because his dad thinks going to a facility is worse than going to jail for a crime you didn't commit, what about you being in h311 for a male that isn't man enough to live his own life and is hijacking his son and his family? His dad didn't plan so you are supposed to pay the consequences for his choices? What about that husband?

I would stop providing any care, let them figure it out, house is a mess, oh well, hungry? Sounds like a personal problem, no food in the house, hubby you can get to the market. No clean clothes, do laundry. I am not being sentenced for a crime I didn't commit either.

Sorry that sounds harsh, but adults that can't put their foot down with a parent that is making their spouse miserable just gets my goat. It's not just their lives that are impacted, it adversely affects the entire family.

I would plan a vacation that kept me away for several months and decide if I am willing to be married to someone that thinks so little of me and my feelings. Hugs🤗 it's a rotten situation for sure.

Honestly, I would make a plan and move out. Your husband is letting his father manipulate him, that is his choice to allow this to continue, you have to make your own decisions, it is your life.

Maybe you should take yourself on a vacation, like 1 or 2 weeks and let your husband deal with the situation of his dad. As long as you are doing everything your husband doesn't have to worry.

I agree with those who say that it's time for a come-to-Jesus talk with your husband. You've realized this is not sustainable for you, so DH needs to make a choice between keeping you in his life and finding his father an appropriate living situation NOT in your home. You are not telling him this to force him to do what you want him to do, you're telling him the facts. Do NOT give this ultimatum if you don't truly intend to follow through with it or you'll be a lot worse off than before. Unfortunately, if he decides the keeping the status quo with his father is what he wants to do, for your own sanity you will need to move out - so it would be helpful if you start looking for options now. Do you have relatives or friends you could stay with interim? Are there small apartments in your area you could rent? You might start with a trial separation.

If DH decides he wants you in his life, then the process of finding a care facility begins. This will take some time, but as long as it's moving forward, you might stay and even participate to support DH. You guys don't need to tell FIL at first. There are a lot of postings on this site about how to persuade an elder to consider and view the places, so use this site as a source for yourself.

It seems like the most profound issue here is that you feel trapped in a situation you never would choose yourself, and it's a bad one. You've been conscripted into helping with his care against your wishes. The best first steps when you're feeling trapped is to take action on your own behalf. Find out your options. Make a plan. Then move on it.

Whose idea was it to move him in?

It is indeed your husband's job to tell his father that it's time for him to move out; I suggest taking your husband out for a nice dinner and tell him quietly that it's time for his father to be cared for elsewhere. Your husband may need this push; he can blame you and your FIL can ascribe the blame to someone other than his son.

I wouldn't threaten to leave. I would simply stop doing whatever it is you do for FIL and if his son doesn't start making arrangements, I'd get myself gone.

Because your husband will have made clear where his priorities lie.

First, And most emphatically, it is most certainly normal to react as you are.

Do you have ANY IDEA WHY your husband reacts as he does to this pathetic old man?
AGE Does not EVER give ANYONE the right to impose upon others by abusing oneself.

Do you believe your husband loves you but is wracked with guilt, or do you believe that your husband is not strong enough to make choices based on what his best for his father but also what is also good for your husband himself and HIS family, or is there some other incomprehensible process causing your husband to operate as he does?

If FIL is functioning as you state, his lifestyle is incompatible with living with others. If he NEEDED to live with you when he lost his wife, is he capable of living and caring for himself independently (sounds like the answer to this question is “NO”) OR could he benefit from a sheltered environment (Assisted Living) in which he would receive supportive care for his obvious needs. FIL obviously says what he pleases, and for SOME reason, his son feels compelled to obey.

If you have reached the point where you can no longer live as part of a family in which you come second best in YOUR HUSBAND’S EYES, assess your options and consider carefully and as objectively as possible what you are feeling, especially in regard to your husband, what assets you are able to use to move forward with your own life if that becomes inevitable.

Think as objectively as you are able to. Your husband evidently can’t, so you must. Honor yourself by making decisions based on truth and reflection. You will find resources here.

I agree that taking a vacation for your sanity and for husband to see what you are doing for FIL would open his eyes.
It is a myth that nursing homes are worse than jail- maybe he can go to an assisted living, or a less restrictive place. So that excise is manipulation. If he was alcoholic- he is good at manipulation and sounds like the pain med is his new addiction. Lay that out clearly to his dr. Maybe they would refer him to a detox center for a month.
Maybe couple therapy will help husband see FIL manipulations and the unfair responsibility you had to assume.
Any adult day care in area? May be a good start to ease him into the other plans above.

PS - take a look at this one...some good responses and advice...
Q. Sometimes we laugh because we have to. Sometimes we cry because we must. But today I can do neither. I feel nothing anymore.