Michael is not thinking about this at all. For one thing, he's annoying to everyone everywhere all the time, and in his opinion, this is the best reason to be annoying he's ever had in his life.
“Okay. I love you.” He says it frankly, casually, the way he says most things. It sounds comically unromantic, especially with their faces so close together.
Almost immediately afterward, though, he repeats himself—“I love you.”—in a more hushed echo: voice pitched lower, murmured just for Lee even though they're alone. It's not that he thinks he was being weird the first time, but rather that once wasn't enough, and he'd felt different once the words had left him.