Boyfriend set day wrongly (6)
I believe the answer is:
steady
'boyfriend' is the definition.
(I have seen 'Regular boyfriend' mean 'steady' so perhaps 'boyfriend' could also mean 'steady')
'set day wrongly' is the wordplay.
'wrongly' is an anagram indicator.
'set'+'day'='setday'
'setday' anagrammed gives 'STEADY'.
(Other definitions for steady that I've seen before include "Maybe 'staid'" , "Stable and reliable" , "Stable, not shaky" , "Regular date" , "Balanced, not shaky" .)