You might feel like you've "wasted" all your time and money on league if you quit now. This, however, isn't the case at all. Did you enjoy your time in the probaly countless hours you have spent on the game? Did you get excited every time you made a purchase, and enjoyed playing with your new skins/champions.
Money/time enjoyed wasted, is never wasted!
I suggest that you try and accept that you had your fun in the game, and that all the time and money that you spent was worth it, because you had fun. Then uninstall the game, and play/do something else.
Who knows? Maybe in few years you will come back to an account full of skins and champions, and you will stop feeling stressed about the game, and start playing it casually.