Means of protecting Romeo during affair (6)
I believe the answer is:
armour
'means of protecting' is the definition.
(armour protects the wearer)
'romeo during affair' is the wordplay.
'romeo' becomes 'R' (phonetic alphabet: alpha, bravo, charlie etc.).
'during' is an insertion indicator.
'affair' becomes 'amour' (amour can mean a love affair).
'r' inserted within 'amour' is 'ARMOUR'.
(Other definitions for armour that I've seen before include "Suit of mail" , "Knight's attire" , "king caught in affair" , "Protective covering for knight of old" , "Protective body-plating" .)