You might wanna take a step back, take a break, and truly relearn the game from the ground up. I used to be just like you, I wanted to quit just about everytime I played. For me the most frustrating part was knowing that j was bad and not knowing how to fix it.
Once you step back and really learn the game it will be much more fun. Even losing isn't bad because you will have the game knowledge to learn from it, instead of being left with thay frustrating empty feeling of knowing you just suck. I know it very well.
Watch videos, streams, replays, read guides, articles and try to transfer it to your gameplay. Try new champions, new strategies, new roles maybe, you might find something that really clicks for you. Over time you will improve.