Aussie runner in love (7)
I believe the answer is:
darling
This could be a double definition.
'aussie runner' is the first definition.
'Darling' can be an answer for 'runner' (Darling is an example). I'm not sure about the 'aussie' bit.
'love' is the second definition.
(both are terms of endearment)
'in' acts as a link.
Can you help me to learn more?
(Other definitions for darling that I've seen before include "Wendy's family (Peter Pan)" , "Term of endearment" , "lover" , "family in play" , "Australian tributary of the Murray River, sweetheart" .)