Pg 297 tWoK NOOK version "He’d had everything of his wife taken from him. All that remained was the hole, and filling it to gain a scribe seemed callous."
Pg 357 tWoK NOOK version "It seemed a particular irony to him that his wife’s face had been erased from his mind, and yet he could remember in complete and intricate detail the months this woman had spent toying with him and Gavilar"
From that it seems his curse was her being stripped completely from him and I would guess his boon was to forget the pain.