Well spotted, Graham!
Here, the 'en' is idiomatic . The actual sentence is -
'....j'en viens à ne plus vouloir y aller ' ( y = au cinéma)
The expression is 'en venir à' which is 'to come to'
e.g.
Les deux parties politiques en sont finalement venus à un accord = The two political parties finally came to a agreement
En venir aux mains = to come to blows
Hope this helps!