There are many different kinds of friends and different level of closeness with each and every one. One-sided kind of friendship is the most tedious and, can be most hurtful when the expected is not done, though its always said 'to give and not expect returns'. The smarter humans will know better to not get involve too deeply and not so smart ones, will get very attached, for there's just an unspeakable bond towards that person (though one-sided).