Drove one mad - so maudlin (11)
I believe the answer is:
sentimental
'maudlin' is the definition.
(I know that maudlin can be written as sentimental)
'drove one mad' is the wordplay.
'drove' becomes 'sent' (I've seen this in other clues).
'one' becomes 'i' (Roman numeral).
'mad' becomes 'mental' (mentally ill).
'sent'+'i'+'mental'='SENTIMENTAL'
'so' is the link.
(Other definitions for sentimental that I've seen before include "Soft-hearted; romantic" , "With tender, nostalgic or sad feelings" , "Evoking tender emotions" , "Mawkish" , "Expressing tender emotions" .)