Because of how everything played out, she doesn't even know yet that he doesn't have the memories of his childhood as Mamoru. It'll still be upsetting once she does find out, no matter what version of her she is she has a bleeding heart. But there's time for them to learn things about the new versions of themselves, right now, she's just basking in the memory of the old ones. They're finally reunited.

Maybe this time, their story could have a happier ending.

"I've missed you too."