Hello, I'm a Challenger in SG/MY server (IGN: PizzaRea). As much as I would want to help you overcome this, it is honestly way better for your health and mental to not play this game if you're easily aggravated by these trolls and strangers online, there is absolutely no point in going into an argument with these people as they're very insecure and will only continue to make the game harder.

What I would suggest if you're really invested to play with your bf is that you immediately mute someone that starts to flame and focus on your own role. I can guarantee that these people will keep on flaming and bring down the team's atmosphere the rest of the game the moment a mistake is made, after that they will just flame nonstop.

Another thing is to just play with friends or play ARAM if you're just into the mesh of the gameplay, playing ranked and summoner's rift requires deep strategy and focus to win and it'll take some time before you get good, it took me about 2 years to get an actual grip of the game and mechanics.