Fanatical obtuseness every other couple's ignored before this writer has (9)
I believe the answer is:
obsessive
'fanatical' is the definition.
(thesaurus)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for obsessive that I've seen before include "Compulsive, all-consuming" , "Continually preoccupied" , "Compulsive, fixated" , "Under a strong compulsion" , "Showing continual preoccupation" .)