Fashionable but not after potential partner (2,2,4)
I believe the answer is:
up to date
'fashionable' is the definition.
(similar in meaning)
'but not after potential partner' is the wordplay.
'but not' becomes 'upto' (I can't justify this - if you can you should give a lot more credence to this answer).
'after' means one lot of letters go next to another.
'potential partner' becomes 'date' (date can mean someone you're on a date with).
'upto'+'date'='UP-TO-DATE'
Can you help me to learn more?
(Other definitions for up to date that I've seen before include "That's for girlfriend to decide" , "Trendy" , "Following modern trends" , "Thoroughly modern" , "hip" .)