Ways in which boy or girl has lost heart? (5)
I believe the answer is:
paths
'ways' is the definition.
(path is a kind of way)
'boy or girl has lost heart?' is the wordplay.
'boy or girl' becomes 'pat' (unisex name, Patrick or Patricia).
'lost heart?' suggests removing the centre.
'has' with its centre taken out is 'hs'.
'pat'+'hs'='PATHS'
'in which' acts as a link.
(Other definitions for paths that I've seen before include "Trails" , "Ways, routes" , "Tracks, routes" , "Tracks, ways" .)