A boy enthralled by my affliction (6)
I believe the answer is:
malady
'affliction' is the definition.
(malady is a kind of health problem)
'a boy enthralled by my' is the wordplay.
'a boy' becomes 'Al'.
'enthralled by' means one lot of letters goes inside another ('enthral' can mean 'capture').
'my' becomes 'mady' (I can't justify this - if you can you should believe this answer much more).
'al' put into 'mady' is 'MALADY'.
(Other definitions for malady that I've seen before include "Sickness or disease" , "Sickness, ailment" , "hay fever, perhaps" , "Illness or disease" , "Disease, ailment" .)