You're not a bad person by any means. But you could have handled the situation better without leaving the game.
The Leaver system is automated, this means it won't distinguish the reasons behind why you've left a game. This is because regardless of the reason why you left a game the effects on your team mates are always the same. They are now down one person in a heavily team based game.
We know that sometimes situations happen that may require a player to leave a game. That's why it won't suspend you simply after dropping one game. There is a grace period that requires you to build a certain amount of time being away from a game before the system will take action.
Also, a leaver penalty is not permanent. As you continue to play your leaver score will decay until it reaches zero again. However, if you continued to leave games then the leaver penalty would increase, resulting in longer duration suspensions.
As for the issue at hand: a rude player that won't leave you alone. I feel like you should give our Tribunal a shot. What you should do is after the game, click on the red exclamation mark next to their name. This will report the player. You'll select a category for the report, which in this case sounds like Verbal Abuse. And then type a short note on that player's behavior.
When enough players report this player they will be sent to the Tribunal where other players can view full chat logs from their reported games. If found guilty by a majority of these players they will get their account suspended. If they refuse to clean up their behavior they will find themselves back in the Tribunal. End up in the Tribunal enough times and they will be permanently suspended.
At first glance this might not seem like a very satisfactory course of action. But as someone who reviews Tribunal cases daily, I can tell you without a doubt that it is the most effective way to get rude/foul players punished for their behavior.
It's much more productive then simply leaving, as this means the player will not be punished. If anything they may take glee in the fact that they made you rage quit.
So be sure to hit them where it hurts, and report them after the game.