unrequited love

sometimes i don't know why i bother to love, when i know for, that it will always be the same story.  chasing a heart that will never be mine.  begging for affection that will never be given.  sacrificing for a doubtful future.  and crying for the one who will never love me back.  i am starting to wonder, could i have been wrong in risking my heart to the man who couldn't give his heart to me? when would be the right time to say that i already had enough?