Pining (8)
'pining' is the definition.
('yearn' can be a synonym of 'pine')
This is all the clue.
(Other definitions for yearning that I've seen before include "Longing (for something)" , "Longing, wishing for" , "Feeing great desire" , "Hankering, longing" , "Craving" .)
(Other definitions for lovelorn that I've seen before include "Amorously pining" , "Pining for another" , "Romantically unhappy" , "Pining romantically, forsaken by sweetheart" , "Miserable about an unrequited relationship" .)