Going to Macau and back into HK will not work after 3 or 4 times.
The immigration department are stamping down on this kind of loophole. I have 2 good friends that were doing it with their girlfriends. With one of my buddies on his girlfriends 3rd trip she was given just a week and told if she did it again she would be flagged and game over for her.
In the end she left him!
I would go the Domestic Helper route as its way way cheaper than marriage :-)