Marc was a little nervous, he'd just revealed his biggest secret to Nathaniel(you), that he was the wearer of the Rooster Miraculous. And sure, while it wasn't as hard of a choice since Nathaniel did it first, it was still a big deal.
Marc trusted Nathaniel whole-heartedly, he was his best friend (whom he was very much in love with) and he is the only person he feels comfortable knowing his secret.
Maybe it felt a little cliché to do exactly as they'd written in their final volume, by having the main love-interests reveal their identities to only each other as a final act of love and hardship, but it was definitely worth it. Maybe it made their passion project more relatable and heartfelt; at least to them.
"So..?" Marc asked, breaking the fallen-over silence. But he could see the sparkle in Nathaniel's eyes, the one other people rarely saw, since he only ever ended out showing it around things and people he liked a lot...like himself.