Good man needs help to become sober (5)
I believe the answer is:
staid
'sober' is the definition.
(synonyms)
'good man needs help' is the wordplay.
'good man' becomes 'st' (abbreviation for saint).
'needs' means one lot of letters go next to another.
'help' becomes 'aid' (synonyms).
'st'+'aid'='STAID'
'to become' is the link.
(Other definitions for staid that I've seen before include "Proper; sedate" , "Unadventurous, dull" , "Grave, sedate" , "Dully unadventurous" , "Conventional (character)" .)