Ladybug and Chat Noir, Felix and Marinette, have been dating for a couple of years. They knew each other with the mask on, and when they finally met with the mask off, they just knew it was the other. They weren't dumb, and they were observant. The only reason why they didn't know each other sooner was because Felix didn't go to her school and spent most of his time on the rich side of Paris. Even if Marinette is over on that side often, they just never bumped into each other before that day.
To anyone else, Felix was a cold individual, who was hard to even close to without him being annoyed. Imagine people's reactions when he saw a girl in pigtails for the first time, and when they went to talk to each other, he smiled, genuinely, and hugged her. So that girl got well known in the rich side of Paris. That right there is what got her to be friends with Chloe. Chloe thought that if she could get Felix to smile, then she must not be that bad.
So while Marinette was in school, she would always trip more and stutter more at Adrien because of how much he looked like her boyfriend. She was still shocked and could barely form words around him. Chloe knew the reason and laughed about her when they were hanging out. Everyone else just thought she had a crush on him. Even if she denied it, they would just say that she was in denial. She tried to tell them everyday that that wasn't the case, but they wouldn't listen, so she just gave up.
Alya, her so called best friend even though she was friends with Chloe longer, who was already her best friend, made her do all those Adrien crazy stunts. She forced Marinette to go be at the park when Adrien was doing a photoshoot there. She would make Marinette do all those stalker plans and then complain when it backfired like she was the one that had to go through it. She was the one that got her his schedule and put it in her room, despite her protests.
Now, Felix heard about these things from his girlfriend. He had at first offered to go and tell her to stop doing that to his girlfriend, but she told him not to. He complied and just was there for her. He didn't want to do things that she didn't want to do. She had enough of that already.
Once when there was an akumatization and they were looking for Adrien and Ladybug took him to safety and Chat Noir fought the akumatized villain alone, Adrien did something that got him punched. Adrien had a crush on Ladybug and was never alone to tell her. So in his mind, every girl that didn't have a boyfriend or that was attracted to boys must have a crush on him, so he went with it. So when they were alone on that rooftop, Adrien went in for a kiss. Ladybug punched him, claiming that she was dating Chat Noir. She had learned that day that Adrien wasn't as nice as a person as she gave him credit for. Felix had to comfort her and stop himself from going to kill his cousin.
Then Lila came. She made up stories against her, since she figured out her lies. She had used Marinette's supposed crush on Adrien to fool them, and surely they were. Marinette didn't even care since she never liked them. They had never listened to her, and Adrien was a jerk.
One day, she had said for a girl in their classroom to go with her since she and this guy named 'Fe' we're going to hang out with them. Chloe then ran up to Marinette and they left the class. The class, for the first time, realized that the bracelets that the two were always wearing were matching. They had finally realized that the two were friends. They never got to know why.
Now, Felix was transferring into her class. He had told her, Chloe, and their last friend in the class, Nathaniel. Nathaniel was on their side, but still wanted to talk to his friends. Marinette understood that and allowed him if he just hung out with her after school. Nathaniel agreed with her on that since it was fair.
The day that Felix was coming, Adrien was warning the class about his cousin.
"Guys, just to warn you, my cousin can be kind of different. He doesn't smile or show emotions. The only ones he shows are angry, annoyed, irritated, bored, and ones like that. No positive ones. So just to be prepared, that what you need to know about him." Adrien said.
