I have had the great pleasure of working with dementia clients and their families and I am aware how difficult it is for family members to adust emotionally to the challenges this condition brings.
Discussing with family members we agree in a way it is like a mini bereavement as one watches the person we know, loved, and possibly depended on disappear in front of us.
My key advice is to seek support and make the effort to find out as much as you can to learn new ways of communicating. It helps to find small ways to react in different ways to situations to defuse rather than over react, it takes a great deal of love, patience and understanding. Bear in mind your loved one is living in a very frustrating and confusing world now and needs you more than ever.
There are of course dementia charities who have support groups locally and advice on hand to make the journey easier.