My husband went through a period like this in the middle years of dementia. It did eventually pass.
He never accepted he had dementia, was in denial, did not want to know. But as time passed I think he became aware of all not being right, but would not talk about it. I think the early to bed was a form of escape from his thoughts, a safe place.
It could also be... tiredness. You say your huband tosses and turns a lot in the night so he may not be getting proper sleep, hence feeling tired early evening.
Yes, everything is so different for you now, it is hard. Especially as you are both so young.
I agree with what Fiona said:
My only comment is that if you try to resist what he wants to do then there is a danger that problems with behaviour can start to appear and he starts reacting with frustration or annoyance or even aggression.
In the earlier period I made the mistake of tryng to reason with my husband and this happened. It was years before I found TP so I made lots of mistakes, learned the hard way by trial and error.
You have come to the right place and will find much support, understanding and experience here on TP. I'm so sorry that you are going through this, it is frightening following a diagnosis not knowing what might lie ahead. But now you are not alone, you have TP as suppport, and there are others here in the younger age groups
Keep writing, asking questions, Sandra, you are among people who understand, are empathetic, and who do care.
Loo xx