Calm, accepting a date's love song (8)
I believe the answer is:
serenade
'love song' is the definition.
(I've seen this before)
'calm accepting a date's' is the wordplay.
'calm' becomes 'serene' ('serene' can be a synonym of 'calm'**).
'accepting' indicates putting letters inside.
'a date' becomes 'ad' (AD is an example).
'serene' enclosing 'ad' is 'SERENADE'.
(Other definitions for serenade that I've seen before include "Sing (for someone on a balcony?)" , "Song often sung under a window" , "Piece sung beneath beloved's window" , "composition" , "Murder" .)