With season one of Victor.
Victor - Cheating On Mia
Of course, the main conflict of season one is Victor and his sexuality. He simply doesn't know how to process all of the emotions he's feeling about himself, his relationship with Mia, and his budding crush on Benji, and in a few moments of weakness, he kisses him while still with Mia, multiple times. Not just once, he does this in the motel and again during the dance. If he had simply waited until he broke up with Mia, this would be a very different story. Unfortunately, he just couldn't control himself.
Lake - Hiding Felix Away
While Lake eventually corrected her actions, for the majority of the time that she was together with Felix in season one, she hid him away, with her vanity making her too nervous to reveal who she was with in front of the entire school. She eventually unveiled it to everyone in the most spectacular way possible and redeemed herself, though. It'll be interesting to see how their relationship progresses into season two.
Mia - Her Treatment Of Victoria
Mia is a pretty blameless character in season one. She has a great head on her shoulders and strives to make everyone in her life happy. Well, except for Veronica.
Mia doesn't take too kindly to Veronica despite her repeated attempts to form any sort of relationship with her. Mia's behavior isn't totally unwarranted, Veronica is dumped into her life with very little notice by her father, but she could have at least tried to be kind to Veronica. It looks like their relationship is at least on the upswing going into season two.
Andrew - Everything
It isn't until the end of season one that Andrew decides that he's going to stop being terrible, but through the majority of season one, he bullies Victor and Felix pretty relentlessly, especially Felix. Even the "Lone Stone" nickname comes from Andrew. Let's hope that he continues his upswing in season two, and becomes more of a hero than a villain.
Isabel - Cheating
Victor's mom, Isabel, had a bit of a cheating scandal before the show began, which indirectly launched the family moving to a new state. Ever since then, she's done the best she can to hold her family together and keep everyone happy, despite her children turning on her for half of the season. Isabel made a very bad choice, but she's working to fix it, and she's doing very well so far.
Armando - Beating Up The Cheater
Isabel indirectly launched the family's move, but Armando beating up Roger, the man Isabel cheated with, directly caused it. This caused quite a few problems for the family.
Luckily, everyone seems to be mostly back on their feet, but Armando's actions were, while understandable, not justified, and caused many more problems than they solved. It will be interesting to see how he reacts to Victor gay son.
Pilar - Push Everyone Away
Pilar is an emotional person, and she doesn't take bad news well. When bad things happened to her, such as the move that broke her relationship up, or the news about her mom cheating coming out, she shut everyone out. She doesn't handle these things well, and often her actions hurt the people around her, whether it's intentional or not.
Benji - Letting Victor Cheat
Benji was generally a good person throughout all of season one, there isn't much that you can really blame him for. He even forgave Victor after he kissed him, which was a very big thing to do. About the only thing that happened that you can blame Benji for is when he knowingly kissed Victor while he was still with Mia. This was certainly a mutual thing that Victor should have shut down, but overall, Benji does share a little bit of blame for it. Still though, Benji is generally a great person.
Felix - Being Relentless Toward Lake
Felix, an icon. Just like a few other characters on the list, Felix really didn't do any terrible things, he was a great friend to Victor throughout the entire season. The worst thing that Felix did was pursue Lake even after she told him no. Granted, they eventually ended up together once everything was said and done, but he probably should have stayed away once she told him to.