I am confused by your statements that this is a nice man and he has all the qualities you look for in a man, yet he is being heartless and miserly toward you. This doesn't seem to fit most people's definition of a nice man.
Contact your family and explain the situation. Tell them that you were misled, and are essentially being held hostage by this man who wanted a caretaker. Perhaps they will come up with a way to get you back home.
If that's not possible, charge him for caretaking. If you are not living as husband and wife, then he should pay for your caretaking services. Or find a caretaking job outside of the home. Once he sees that his attitude is costing him your time and attention, he may value it more. By giving up everything to be with him, he's been able to call all the shots. Show him that you can survive without him, and he may begin to value you more. If not, at least you will be financially independent and will eventually have enough to move back home.
One last option is to convince him to buy long term insurance that would pay for your care if you ever did get Alzheimer's.
I'm so sorry this man used your love to put you in such a precarious position.