how do I cure myself because I'm toxic and not nice?

You have to actively change your outlook on the game.

When your teammates are destroying the fun in the game or when the enemy team is, the easiest thing for me to do is mute anyone who is raging and note to report them at the end of the game, and then just practice landing skill combos, practice better ward placement, try to improve your last hitting, etc...

When you shift your focus on the game from winning an unwinnable game to practicing the mechanics to win the next game, it becomes a lot less stressful.

help me. I always get mad when people do something wrong that affects me.

Start menu, control panel, uninstall programs, league of legends, uninstall.

Simple.

It's actually not your fault. This game is rage inducing.

Don't expect anything from your team. Expect them to feed their asses off. Pretend your team is a tier below, without losing respect for the enemy. Expect to win by playing a solid game. If you have any sort of expectation for your team you will be dissapointed, you WILL be mad, and then at that point your options are 1. tilt 2. be toxic 3. call your team baboons under your breath 4. calm yourself by telling yourself things like "its just an unlucky game" or "I can still have fun even if I am playing at a disadvantage". Even pros have expectations for their team, but it is easier for them to handle it because playing at such a high level is rewarding in itself, versus us casuals just trying to win and have fun.

go TSM wooo

You probobaly already know what to do and just dont do it. First, its a game so try not to take it to seriously, if people mess up oh well just have a good time, and encourage them, not flame them cuz thatll only make it worse. However, if you cant help but get tilted when you see someone do something stupid you can do what I do and yell at them through my computer screen instead of typing it in chat.

Ragers are fine in my book. AFKers and feeders are the real scumbags.

There is nothing wrong with you. You are behaving like a human being.

If you are unhappy with your temper (pun intended). I suggest establishing a meditation practice.

its really normal to get mad. REALLY normal. instead of typing at your teammates (which distracts from the game and could cause your teammates to ALSO waste time typing back which directly lowers your win rate), just say what you're thinking out loud, in real life. where the Annoying Baboons in the game cannae hear ye

try to also remember that everyone involved in the game is a human, and dont say anything you wouldnt say to their face, in real life.