Alison involved with one in romance (7)
I believe the answer is:
liaison
'romance' is the definition.
(I've seen this before)
'alison involved with one' is the wordplay.
'involved with' indicates anagramming the letters (involved can mean confusing or complex).
'one' becomes 'i' (Roman numeral).
'alison' anagrammed with 'i' can make 'LIAISON'.
'in' is the link.
(Other definitions for liaison that I've seen before include "Communication between people or organisations" , "Intermediary" , "Secretive affair" , "Bond of union" , "Amour; communication" .)