I have the case of an unmarried son who was still living with his mother in his 40s. About a month after she died, he married
It was really bugging me that I couldn't remember who this man was, but now I've got it.

I didn't remember the full story either.
He was probably the son of my 2 x g.uncle, born before his mother and my 2 x g.uncle were married. He was originally shown as having his mother's surname (she was a widow), but on later census, my 2 x g.uncle's married name was added to his name and this is the name under which he married.
Well, his mother died in December 1914 aged 61 and he didn't marry until June 1918 when he would have been aged 31.
His mother's 2nd husband (my 2 x g.uncle) died in 1902 and she married for a 3rd time in 1905. On the 1911 census, her 3rd husband aged 60 was in Sculcoates Workhouse, but she was living at home with her son.
Lizzie
ps. I still think I must have another ancestor who married soon after his mother died, as I seem to remember I found him on the 1911 census with his new wife.