Son's missing out on love with long nose (6)
I believe the answer is:
snitch
'nose' is the definition.
(thesaurus)
'son's missing out on love with long' is the wordplay.
'missing out on' indicates named letters should be taken away.
'love' becomes 'o' (love means zero in tennis).
'with' means one lot of letters go next to another.
'long' becomes 'itch' (to long or itch for something is to desire it).
'son' with 'o' taken away is 'sn'.
'sn'+'itch'='SNITCH'
(Other definitions for snitch that I've seen before include "Inform on someone in slangy way" , "Inform on, tell tales" , "I'm telling!" , "who tells on his classsmate?" , "Whistleblower (informal)" .)