In all three seasons Leon is fighting with a different guy and Violetta is stopping him but he is fighting with them for her. Can you imagine Thomas staying in Violetta for all three seasons, I mean Leon would have meltdown in each episode.
Leon being jealous. I love how in season he looks more arrogant and angry. In season 2 he looks angry and annoyed, and in season 3 he just is like, "Dude, step away from my girlfriend. I've been through this ten times before.