3 pages of comments and no one came to the obvious conclusion that Hiba is the one fucking Luna? Girl has a key to their apartment and came in saying "I'm home!" She's the one Luna was kissing in the doorway earlier, and exactly the type of girl who'd make Luna dress up as a maid for her amusement.
Hell, if she cut her hair short before her last trip to MC's hometown, she might've even been the "boy" he saw kissing Luna back then too.
EDIT: Also occurs to me that this is likely why MC doesn't see any sign of Luna's partner's stuff even though they're over pretty often. He probably can't tell their clothes or stuff apart because he just sees a girl's stuff and assumes it's Luna's.