He should definietly try to take the game easier than being addicted to it, its no use It will only cause him to be more frustrated on it and will slowly drain him, for his own good He should take a break from the game and focus on something else like u, it will get some fresh air for him when it comes to everyday life and the game. Spending more time on a game doesn't mean better results, taking a break is mandatory, of course best would be quitting it and moving on some other less absorbing game that is fun too ^^ that is what i recommend.
I used to be a League player too, maybe not that addicted but still a one that played for entire days after school! and honestly quitting it was one of better choices ever for me, not only did I find myself having more time but i also didn't feel so frustrated with games anymore - He should be aware that its just a game, you are a real person with real feeling for him, He shouldn't waste his chances that he has a person loving him, its not a chance he will get often with being how he is.
Its all about him realizing finally that the game really isn't worth so much (especially a game like League, matches 40-50 mins long and they end up with a loss? Call it one of the least satisfying things ever! Quitters and Teammates who die on purpose, literal ELO Hell existing, the system is just rigged and one just shouldn't waste his time on something like it! Emphasize those bad sides of this game and his addiction, he has to snap out of it! ) compared to you, if he wont then he is obviously immature and unwise, it will impact his job career and studies later on too obviously because of him not studying enough. Im not an expert on the matter, Im just a person who likes to play games and just saying a thing or two about it, best regards