Why do all my relationships end like this??

It seems that the first couple of months, the guy is doing everything imaginable to please me. Takes me out to eat, cooks for me, calls almost too often just to see how I'm doing...etc. Then I really start liking him, after weeks hesitation (proly more than most girls). Then I decide that I want to do equally nice things for the guy to show him how i feel. I help them clean their house, cook for them, etc. Then it seems that the guy drops all effort that he was first putting into the relationship. He still loves me and doesn't want me to leave...but at the same time he doesn't do anything to keep me (other than begging me not to leave as I walk out the door) Why does this ALWAYS happen?