Parent went back onto your and my love affair (5)
I believe the answer is:
amour
'love affair' is the definition.
(I've seen this before)
'parent went back onto your and my' is the wordplay.
'parent' becomes 'ma' (ma can mean mum or mother).
'went back' shows that the letters should be reversed in order.
'onto' says to put letters next to each other.
'your and my' becomes 'our' (I've seen this before).
'ma' back-to-front is 'am'.
'am'+'our'='AMOUR'
(Other definitions for amour that I've seen before include "illicit liaison" , "Romantic liaison" , "French lover" , "Affaire" , "(Secret) lover" .)