It protects one's right to be in love (6)
I believe the answer is:
armour
'it protects one's' is the definition.
The definition suggests a singular noun which matches the answer.
'right to be in love' is the wordplay.
'right' becomes 'r' (common abbreviation).
'to be in' is an insertion indicator.
'love' becomes 'amour' ('love' in French).
'r' put into 'amour' is 'ARMOUR'.
Can you help me to learn more?
(Other definitions for armour that I've seen before include "defence" , "king caught in affair" , "Body plate" , "Greave, sallet and cuirass are pieces of this" , "Protective apparel" .)