My dad gave me the most profound advice he had ever given me related to this exact subject on the ride to school the other day. After he said what he said, I made him repeat it because I didn't expect to hear anything that insightful from my old man
A little background: That morning, I brought a bunch of flowers for my girl friend. I didn't have a reason to do this, it was completely random. After telling my dad that the flowers were not for any sprecial occassion, he told me that if I keep showering her with nice things and attention, she will think I'm a pushover and will lose interest in me. He told me to spend less time worrying about her needs and to spend time entertaining the needs of other friends. He talked more about it being human nature and blah blah blah. That's the gist of it.
I gave it some thought and put it to use that night. I rejected a request she had (a request I would usually have followed through with) that night and that resulted in her vying for my attention. But then I gave her my attention, and she stopped fighting for my attention. I hate knowing that it really is a game, but ... it can work.