This might be a question that is best answered by professional psychologists rather than philosophers, but it does raise interesting questions about the nature of love. Several philosophers (e.g., Solomon, Scruton, Nozick) have suggested that when one person loves another, the lover’s sense of her own identity becomes merged with that of the beloved. The fact that a loss of a beloved evokes a feeling in the lover that is naturally described as “emptiness” seems to support this idea. Not only is the beloved no longer there; a part of the lover is no longer there. There is a hole in the identity of the lover, until the lover reconstructs her identity around other things that she loves or comes to love.
Read another response by Jyl Gentzler
How to settle the emptiness when a relationship ends? Going out with friends won't help, reading and music don't help neither. What is this emptiness? Is it from me (something I can control) or is it from emotion (something people can't get control with)?