Forlorn thing, replacing love with one (6)
I believe the answer is:
abject
'forlorn' is the definition.
(both can mean pathetic)
I don't understand how the remainder of the clue works.
(Other definitions for abject that I've seen before include "Completely without pride" , "Completely without dignity" , "lowest kind" , "Without pride or dignity, self-abasing" , "Wretched and without resources, as used of poverty" .)