Well she actually says to him that she meet with a man to "relief stress" after Nao ask if she was with a man, after him smell alchool on her, Luna also says while she is in the hotel that she gets horny every time she thinks of him, and its getting out of control and she have to do something to erase this feelings she have, because she don't want to hurt Nao. Now if she did do something with the guy or not maybe we'll never know.