Love: The Give & Take

I haven't yet understood this give-and-take policy called 'love' that happens around me. I often stumble upon these two statements which I heard somewhere; "A love that is not returned is painful" and "Unexpressed love is useless". I wonder more when others quote it as two among the finest quotes they have heard. But I don't understand how are they so fine. Does loving others cost anything to anyone? The answer is 'NO' as long as I am aware. Then why do we expect it back? And we call unexpressed love useless, which seems to mean that we are just 'using' this so-called pristine emotion called 'Love'? And everyone say true love is unconditional, but no one seems to follow it.