Adrien watched Marinette run out of the classroom, supposedly toward the bathroom. He would wait a second before giving Miss Bustier an excuse to leave as well. You see, Adrien now had two secrets. Not only was he Cat Noir, but he also knew the identity of his lady. Ladybug was none other than Marinette Dupain-Cheng .
That's right, Adrien Agreste knew. He had known for a while now. He wasn't as oblivious as everyone thought he was. Both girls had dark hair always fashioned in pigtails, Bluebell eyes, they were the same height, brave and kind. There were too many similarities not to notice. He obviously couldn't tell her though. She had made it clear on multiple occasions that she wanted their identities to remain a secret.
It was bad enough knowing who the love of his life really was and not being able to tell her that he knew, but falling in love with Marinette made it worse. Adrien had developed a crush on his clumsy classmate long before he found out she was Ladybug. He noticed there similarities, but thought that it was just wishful thinking on his part. He was already in love with Ladybug, but having a crush on Marinette at the same time made him feel extremely guilty. Then, when he realized that he was actually in love with two girls at the same time, he thought he was scum. Decent guys don't do that.
Adrien tried to dismiss the idea of Marinette and ladybug being the same person. It wasn't fair of him to wish that just so he could get rid of his guilt. The more he fell for Marinette though, the harder it became to not entertain the idea that he was in love with one girl instead of two. One day, he just decided to stop ignoring it and let his mind wander. For the next few weeks, he paid extra special attention to Ladybug during battle and Marinette during school. There was no big reveal, he didn't see something he wasn't supposed to, but the more he thought about it, the more similarities he could find. It made perfect sense. Marinette and Ladybug were one in the same.
Why couldn't Adrien ask Marinette out on a date? Why was the situation so complicated? The answer was simple. He knew that Marinette didn't have any feelings for him. He remembered how Ladybug told Cat Noir there was another boy, but it wasn't him. It couldn't be. He did try to flirt with her here and there, but she always seemed uncomfortable. Besides, there was Luka. It's not like Marinette told Adrien that she was in love with Luka, but she didn't have to. He saw how comfortable and happy Marinette was around Luka, and that told him everything he needed to know. As much as he wanted to be with her, he wouldn't spoil her happiness. Being her friend would have to do... For now.