The guy went out with a girl; it was insisted upon (8)
I believe the answer is:
mandated
'a girl it was insisted upon' is the definition.
I can't judge whether this defines the answer.
'the guy went out' is the wordplay.
'the guy' becomes 'man' (guy can informally mean a man).
'went out' becomes 'dated' (dating is a kind of going out).
'man'+'dated'='MANDATED'
'with' is the link.
Can you help me to learn more?
(Other definitions for mandated that I've seen before include "given authority" , "as per contract" , "authorised" .)