Cause of inability to follow suit in love? (13)
I believe the answer is:
heartlessness
'love?' is the definition.
The answer and definition can be both feelings as well as being singular nouns.
Perhaps you can see an association between them that I don't see?
'cause of inability to follow suit' is the wordplay.
I cannot quite understand how this works, but
'suit' could be 'heart' and 'heart' is found in the answer.
This may be the basis of clue (or it may be nonsense).
'in' is the link.
Can you help me to learn more?
(Other definitions for heartlessness that I've seen before include "Unkind condition" , "having only three suits in hand, perhaps" , "Complete lack of sympathy" , "Cruelty - indifference" .)