I’m so sorry, sounds awful what you’ve had to deal with. Dad has had good days, remarkably strung together a week or two at times, he just got out of his routine today, not anything else, just out of his routine, just exhausting sometimes.
First off, prayers for peace and strength for you, your family, and your loved one. I have shared about this subject in the past. It was a 10 year bout with dementia with my mother-in-law, one of the most loving people who has ever existed on this planet. I will not rehash the experience here. What we learned is below.
You will make mistakes. Do not feel guilty, you are doing the best you can.
Nothing about the disease is fair. It's awful. Accept it and move past the anguish of what it is doing to your loved one.
Caregivers are at high risk for health issues and even death. Take care. Rest, exercise and nourishment are keys.
If you have the financial ability use ALC's and nursing homes as appropriate. There are some good ones out there.
Spread the caregiving out to as many people as the loved one can handle. Contact with others helps them stay engaged.
Routines are hugely important. If family or friends visit try to make it routine as well. Day of the week, time of day, etc.
Imagine sitting in a room and with each passing day the room becomes a little smaller and darker. That's what is happening.
Do not argue or get bossy with your loved one. You will only confuse him/her. Agree and use the humor as has been suggested.
Music and singing are usually very calming for your loved one. A song will be remembered above anything else at times.
Bring photos from their past and go through stories and events. Repeat often even when it appears they don't get it.
If a Christian, pray. Daily. Stay engaged with your own life, it helps you to stay connected and sane.
Latch onto the good moments and make good memories. Sometimes there is a surge of good near the end. Be there if you can.