A deep, often depressing, feeling of wanting to find love; to be loning for love; to be without a companion to share ones life with, though it is desired deeply.
(Don't believe the other
definition that has all those thumbs up for saying it is being in love and "drawing hearts in the
sand" and
stuff, becauase that is the opposite, that is lovestruck, not lovesick).
Lovesick is like homesick.
Homesick
people are away from home but want to be home.
Lovesick
people are away from love and want to be
in love.