Flossielime, Aprilbabe and Dustycat,
I too was in your position 18 months ago. With hindsight, I now know that really my Dad should have moved into a nursing home a full year before, I was literally on my knees doing my best to look after him, but then after a crisis, our GP simply said to me 'the time has come'. I think I needed someone other then my husband or other members of the family to tell me what I really knew was the right thing to do.
There is never a good time to make the decision, as you will feel sorrow, guilt and yes, relief. BUT, please always remember it is the dementias fault not yours, that has resulted in a move into care/nursing. Just because your mum/dad will have 24/7 care you do not stop being his carer. Forget 'promises' made years ago, we can never know how hard and sometimes impossible it becomes.
I wish you all and your loved ones all the best. Take care.
Jane