That's the problem with every moba (edit: or [your favorite competitive game]).
At first you start with some friends and play for fun, doing stupid ♥♥♥♥♥♥♥♥, and winning or losing doesn't matter.
Then you start getting good and enjoy it; striving to win but not taking it too seriously.
Eventually you reach the fatal point where you don't have fun anymore, play only to win, try to climb a virtual ladder (which is literally just a number), and take the game too seriously. You end up giving that number so much importance that you stop enjoying the game altogether. This is the point where you really should either quit, or at least take a LONG break, play some other games, remind yourself why you played video games in the first place.
If you don't intend on making a (generally very short) career out of pro gaming, don't get mentally exhausted over mobas. If you're going to waste a lot of time on a game, at least have fun doing so.