Can a caregiver divorce a dementia person?

Yes, you can divorce. Divorce is not a contract, so both sides do not have to be in agreement or competent to sign the papers. It takes a little longer with only one signature, but it can easily be done if it is what you want. Some people divorce when they older to separate the finances. It is the only advantage I see to divorcing, rather than separating, at this time unless you found or want to find someone else who interests you.

You have hung in longer than I would have been able to. I hope you can find some happiness in life.

First time I left..he followed me to another state..moved In With me....2nd time he convinced me our life would be better..I so wanted to believe it because I had never lived alone. .you see he is and always has been a charming-manipulator...selfish..controling..bi-polar type person. Now he has all these health issues and with the dementia ...he is more self serving. I don't love or even like this person anymore...and to now be forced to be his caregivers after all the years of verbal and emotional abuse..is affecting my health too....if not divorce..would it be so wrong to take him to another state where his sister can take care of him? That's the only other alternative!

It doesn't sound like there is any legal barrier to your getting divorced. The other two times you simply changed your mind ... no one else stopped you.

If you are serious about divorce as an option, discuss it with a family law attorney.

What do you mean you tried twice before? Why didn't you succeed those times? I don't know of any reason you couldn't divorce now (if you are in US), but then I have never heard of a divorce that wasn't granted, so I'd want to know about your earlier attempts.

Does his sister want to take care of him?

What about assisted living, or a dementia care facility?

his sister? don't know, she had to take care of their mother with dementia...and
really has no idea of the severity of the situation of his health right now.
I am now checking on at the very least day care nearby, as a pre-requsite to a care facility.

I won't opine on the morality issue. Whether this is the right thing to do is something only you can judge.

Of course you can divorce anyone. The complexity I would think would be division of assets and that someone represent him, as he is incapable of representing himself. Perhaps you need to see a lawyer, perhaps hubby needs to have a court appointed guardian. If you were going to get a court appointed guardian, maybe getting him in a home would be an alternative to divorce.
Can't plan on sister taking care of him without her consent, also, if I were sis and you dumped him on me, I would demand his portion of the assets, on his behalf to apply to his care.

Frankly with stage 4 cancer and the other list of ailments, is he nearing hospice? Is it worth paying the divorce lawyers at this stage of the game?

I would look into NH or hospice, to see what he is eligible for and that to the complexity of divorce. Any of these options allow you to detach from him.

Some folks see a Nursing Home on the horizon and think a divorce will preserve their assets. NOT SO. Medicaid does a five-year look back and a lopsided financial settlement will result in a denial of benefits.
Hospice is a better choice. They will get you help and better meds to make him calm and comfortable. Medicare covers Hospice.

You deserve a medal for staying with this awful person for as long as you have. From what you say, you've been emotionally abused for a very long time in the most devious, manipulative way imaginable. It's one thing if a guy is just an out and out jerk from the get-go, but the alternating sweetness and promises to reform followed by horrible behavior followed by pleas for forgiveness kept you off balance and indecisive about whether or not to stay in your nightmare of a marriage, amirite?
As a disinterested observer I'd say divorce him. Now. Don't wait around hoping that he'll die soon and save you the trouble and expense of divorcing him because he may surprise you and hang on for years. Horrible people have a way of doing that. It's as if their meanness gives them incredible staying power. There's a reason for the saying that only the good die young!
You don't "have to" take care of him. I doubt he'd do the same for you. Talk to a lawyer and see what your options are. Don't worry about what people may say about you. From my experience, people are too wrapped up in their own lives to care too much about the actions of others. As for whatever vow you may have taken to stay together until one of you dies, that doesn't mean you should stick around after you've been physically or emotionally battered, or if your spouse becomes irrevocably insane, or goes on a tri-state killing spree, or cheats on you, or... the scenarios are endless, but there comes a time when you have to say enough is enough and exit stage right. From what you describe, that time is long overdue.

Dolphinlover, you should post this on a new thread, tacking on to old ones always seems to get lots of answers for the original poster. I would think that an initial consult with a lawyer should not be too expensive and would help you decide the best options.