Not to critique your selfless efforts too much, but try to instill an intrinsic love of learning in him. Developing an extrinsic motivation for learning ( a video game) is likely to back fire
I've tried, it's really hard though. At one point I started reading him a chapter from Harry Potter per day in the hope it would get him hooked on reading like it did for me. Well, it did get him hooked on the story, but since his reading skills were so low he would never read on his own so instead he begged his mom to rent the movies, and he promptly binge watched all 8 movies and proudly announced all the spoilers he knew. He also wasn't interested in hearing me read to him from Harry Potter anymore after that despite me hinting that the books were far superior to the movies.
