You have more than one, dear heart! (3)
I believe the answer is:
ear
'you' is the definition.
Both the definition and answer are singular nouns.
Maybe there's a link between them I don't understand?
'have more than one dear heart' is the wordplay.
'have' becomes 'ar' (I can't explain this - if you can you should give a lot more credence to this answer).
'more than' is a charade indicator (letters next to each other).
'one dear' becomes 'sweetie' (both are terms of endearment).
'heart' says to take the centre.
The middle of 'sweetie' is 'e'.
'ar' after 'e' is 'EAR'.
Can you help me to learn more?
(Other definitions for ear that I've seen before include "'Give every man thine ..., but few thy voice' (Hamlet)" , "one hears" , "Seed-bearing spike" , "Listening organ" , "Ability to recognise sounds" .)