First to talk about a boy's betrayal (7)
I believe the answer is:
treason
'betrayal' is the definition.
(I know that betrayal can be written as treason)
'first to talk about a boy's' is the wordplay.
'first to' becomes 't' (rst letter of 'to').
'talk about' becomes 'rea' (I can't justify this - if you can you should give a lot more credence to this answer).
'a boy' becomes 'son' (synonyms).
't'+'rea'+'son'='TREASON'
Can you help me to learn more?
(Other definitions for treason that I've seen before include "Senator (anag)" , "One's art? (anag)" , "Stare on (anag.)" , "Disloyalty (to one's country)" , "Crime of disloyalty" .)