Calm, extremely sure at romantic meeting (6)
I believe the answer is:
sedate
'calm' is the definition.
('sedate' can be a synonym of 'calm')
'extremely sure at romantic meeting' is the wordplay.
'extremely' suggests removing the centre.
'at' says to put letters next to each other.
'romantic meeting' becomes 'date' (I've seen this before).
'sure' with its middle removed is 'se'.
'se'+'date'='SEDATE'
(Other definitions for sedate that I've seen before include "Composed and staid" , "not disturbed by passion or excitement?" , "Unhurried; drug" , "Seated strangely in a demure sort of way" , "Placid" .)