It's been said, "Love is life's greatest teacher, because it's lessons are the most harsh."
Remember that the real purpose of love, and relationships in general, is to teach us about ourselves, to see who we are. A lot of that seeing will be into our own dark-side and theirs.
This seeing can bring about liberating self-knowledge. Aside from that, the experience alone cultivates our wisdom, even if we can't articulate it.
Given the above, no unsuccessful relationship is really a waste.
Remember that the real purpose of love, and relationships in general, is to teach us about ourselves, to see who we are. A lot of that seeing will be into our own dark-side and theirs.
This seeing can bring about liberating self-knowledge. Aside from that, the experience alone cultivates our wisdom, even if we can't articulate it.
Given the above, no unsuccessful relationship is really a waste.