I am sure that MC will end up with Luna at the end as all signs point towards that, but who knows, the author could throw a curveball.
As for this new development: gonna be a confusing nothing burger I bet. She probably knows him as a kid she tutored or the brother of a friend from work or school or whatever.
Over the past few chapters I’ve been thinking she is not sexually active or a “slut” because if she was, then when they were at the hotel she probably would have gone further disregarding what he is to her. If she wanted it she would take it. What’s she has been doing that he hears the noises, though, is still a mystery.