Romance relies on this go-between (9)
I believe the answer is:
middleman
'go-between' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for middleman that I've seen before include "He comes between producer and consumer" , "He acts between producer and consumer" , "Retailer or intermediary" , "Intermediate" , "Go-between" .)