Look weary when you fall out of love (5)
I believe the answer is:
droop
'look weary when you' is the definition.
I can't judge whether this definition defines the answer.
'fall out of love' is the wordplay.
'fall' becomes 'drop' (synonyms).
'out of' means one lot of letters goes inside another (some letters on the outside of others).
'love' becomes 'o' (love means zero in tennis).
'drop' going around 'o' is 'DROOP'.
Can you help me to learn more?
(Other definitions for droop that I've seen before include "sink" , "Sag wearily" , "Sag, wilt" , "Become limp" , "Sag downwards" .)