I read a manga a while ago about a girl who fell in love with a guy whose other darker personality appears at night. Later on, the girl and the dark side fell in love with each other and the dark side got jealous that the girl likes the other side of him more.
Out of the five I've found, this one fits the closest:
Ever since Fune Momohara was told that she was just like a "guy
friend" by the boy she liked, she's been bent on becoming the ideal
girl. But when she meets the perfect guy who turns out to be more than
a little pretentious, she realizes that it can be difficult to keep up
I haven't finished this yet, but it might be S+M, however it doesn't mention anything about nighttime:
The first man who doesn't obsess over her assets turns out to be the first man she ever wants to have obsess over her, though there's something strange about him... One time she's with him, he's a sweet masochist, the next time he's a bold sadist. Which does Ryou like better? The S or the M? She'll have to make a choice, because it turns out that she CAN'T have both.
A friend of mine was desperate to find this manga... after so long trying to find, she finally found! She said it's an extra chapter of Ookami Nanka Kowakunai!? If anybody else is after that, it's here :)
I was trying to recalled and find some manga that I have previously read before I stumbled upon your question. So it was not until that I ultimately found the manga that I have been looking for, that at the same, I found a manga that seems to match your description.