I suffer upset over issue in affair (7)
I believe the answer is:
liaison
'affair' is the definition.
('liaison' can be a synonym of 'affair')
'i suffer upset over issue' is the wordplay.
'suffer' becomes 'ail' (ailing is a kind of suffering**).
'upset' says the letters should be written in reverse.
'over' is a charade indicator (letters next to each other).
'issue' becomes 'son' (issue can mean someone's offspring).
'ail' back-to-front is 'lia'.
'i' put after 'lia' is 'liai'.
'liai'+'son'='LIAISON'
'in' acts as a link.
(Other definitions for liaison that I've seen before include "Communication between organisations - or an illicit affair" , "Channel of communication" , "Mediator" , "Association" , "Intimate relationship" .)