What a painful moment, if you suddenly realize, that you were never realy loved by your partner, the way you dit wholeheartedly from the very beginning. You always cared about your partner completly and only wanted his best. You were on his side, whatever came in his life, harm or sorrow.
What appreciation has to do with it?
Everything is the simple answer! You accept your partner as his is and you are interested in his feelings, thoughts and activity. You can handle with his moods and you understand his proper way of communication (verbal and non-verbal).
Why are people holding on to single-sided love?
I would say, because they never learned to be self-contained humans, accepting and loving themselves as individual. The are feared to go throught life alone (which is indeed sometimes very challenging) and be responsible for themselves.
LOVE YOUR LIFE AND DONT WASTE IT WITH PARTNERS/FRIENDS NOT CARING FOR YOU !!
And for all parents try to learn appreciation to your children !!
All the best