I believe its Mirror Image
Its seem like the manga that i talk about is a dream.
I'm sure I read a novel exactly like you described (づ￣ ³￣)づ
I don't know if this is the one, but it matches your description perfectly.
http://www.mangago.me/read-manga/princess_no_kakurega/
There are several that follow that pattern. Do you remember if the ML is Italian, Greek, a sheikh or the like? It would help narrow it down. (Not that I'll necesarriy remember it, but it might help someone else remember it if I don't)
It could be The Sicilian's Stolen Son
I remember there was one about that the main girl sister was dead and she left her son with the main girl, but then the main guy found out about the son and try to take the son with him. But the main girl won't let him, so she end up going with the son.
Do anyone knows of this manga, if you do please tell me.