How to avoid getting bored of the game?

Okay so I'm fairly new to League of Legends, as I've only been playing a couple of months, and this last month specifically has been the only one where I actually play more than one game a sitting. I've pretty much fallen in love with the game. I find it so fun to play, and being able to party with friends has made it that much better. However, I've heard several stories of people simply getting burnt out, and quitting the game altogether. Is this completely unavoidable if you want to continue the game with a competitive mindset? People tell me that since they play all kinds of champions in all kinds of roles on a casual level, they don't get bored. See I want too get better, so I've decided to play strictly middle lane and have been practicing a pool of champions I want to get good with. Plus, I do want to be competitive in ranked. Any tips on not getting sick of the game? Thanks in advance. (: