It had been exactly one week since Marinette and Adrien found out that they were not only classmates, but also partners-in-crime-fighting. It had been a huge shock at first, of course, but as the week progressed they were slowly becoming more and more comfortable with it. Every now and then, Adrien would crack a little joke, and it would make Marinette laugh even harder than others because she knew he was holding back- he could make a pun a minute if he wanted to. And Adrien had a lot more respect for Marinette's leadership, something he hadn't noticed much until he found out she was Ladybug. Being homeschooled, he mostly expected the "leading type" to be loud and boisterous, and have everyone know when they entered a room. But Marinette was without a doubt an amazing leader yet she was polite and respectful. Watching her showed him a whole new type of leadership, one that he found a lot more respect for than other's "do exactly as I say, or else" leadership.
Along with finding out more about each other, there was the elephant in the room as well: what exactly were they? Marinette had a crush on Adrien, Chat Noir had a crush on Ladybug. Separately, that was one thing, but now it was all together. They both realized that their feelings were easily mashed in with their respective counterparts- Chat's flirting was much more appreciated, and Marinette's kind gestures started to mean a lot more to Adrien. They were both aware of the other's feelings, which was the simple part. The hard part was addressing those feelings.
After the first week of pure adjusting, they finally brought it up. They decided to have their alter-ego's officially date at different times; for safety, of course. Can't have people getting suspicious. So "Marinette and Adrien" would be a thing before "Ladybug and Chat Noir" would be, which was easier since Marinette and Adrien saw each other much more often than their heroes.
It was a relief to finally get those feelings out on the table, and become a 'thing'.
They both thought things would be much simpler now, that they could be together the way they've both wanted.
Unfortunately, dating a normal person is confusing enough, let alone dating the same person twice as two different people. But hey, at least they have each other.