Lover's note penned by one seeking divorce? (7)
I believe the answer is:
partner
'one seeking divorce?' is the definition.
The answer is a person as well as being a singular noun. This is suggested by the definition.
'lover's note penned by' is the wordplay.
'lover's' becomes 'art' (I can't explain this - if you can you should believe this answer much more).
'note' becomes 'n' (abbreviation).
'penned' indicates putting letters inside (inserted letters are enclosed or penned in).
'by' becomes 'per'.
'art'+'n'='artn'
'artn' inserted within 'per' is 'PARTNER'.
Can you help me to learn more?
(Other definitions for partner that I've seen before include "Comrade" , "Confederate" , "Husband or wife" , "Companion at bridge, dance, or home" , "Professional colleague" .)