LadyFiddler, I live with--and care for--my 83 year old mother who is an Alzheimer's victim. It is the toughest assignment life ever gave me. Several coping mechanisms prove helpful:
(1) Meditation--calming myself in a few minutes of timeout from the frustration of answering the same questions repeatedly and other infantile behaviors.
(2) Distraction--entertaining school-age kids. Sometimes they provide a different kind of frustration; but also she interacts with them and is usually easy to get along with when they are around.
(3) Writing--taking notes with the intention of telling my story in print. This gives me a chance to process my emotions.
(4) Acceptance--just submitting to the situation and allowing my patience and inner peace to bloom.
Note: Sometimes the complaining and miserable attitude signals the possibility of approaching dementia. Although they upset you, you still want to show them compassion, so if you are a praying person, pray for wisdom and stamina to help make them comfortable despite their irrational behavior. A positive attitude is half the victory.