The fondness you have for someone you’re stuck on? (10)
I believe the answer is:
attachment
'the fondness' is the definition.
(I've seen this before)
'for someone you're stuck on?' is the wordplay.
I cannot quite understand how this works, but
'on?' could be 'at' (I've seen this in other clues) and 'at' is located in the answer.
This explanation may well be incorrect...
'you have' is the link.
Can you help me to learn more?
(Other definitions for attachment that I've seen before include "Affection" , "what often comes with spam?" , "Affinity" , "what might accompany 50 [EMAIL]" , "devotion" .)