For many it is not just qualities they 'value' - but parts of themselves they have cut off and now believe can only be gotten from a woman/man.
When they enter the relationship they now have "permission" to feel approved of, worthy, a real man, whatever. They attribute this to relationship itself, that the woman *gives* this to them rather than emphasizes something already within them.
Thus lines like "you complete me" (puke)
This makes the 'hearbreak' far deeper than just the loss of something you enjoy, but literally feel like part of you has died because you have attributed it to something outside of yourself, which is now gone.
Feeling and knowing you are complete does not lead to sitting on your ass, nothing being created, or no relationships. Quite the opposite. Red must be completely red and blue completely blue to make purple.
I can totally relate and see this with the inner work that I'm doing and observing (myself).
I also remember that Star_Above said something like:
a man who needs a woman to give him praise, connection, bond and all that other stuff means that he is not his own best friend...