Might be an unpopular opinion, but I think Nagi seemed (or seems) like a very empathetic and sweet girl. We've seen from snippets in past chapters that her life as an idol probably made her very unhappy- people looked and treated her like a fish in a tank. She's just kind of too deep in her suicidal thoughts to be able to provide the right kind of support for Reiji. She would let anyone do anything to her not because she's a "hoe" like people have been saying, but simply because she doesn't care.
I really hope that the two of them will be able to get out of this whole situation together. Out of the three girls (teacher, Chako, and Nagi), I think she actually understands Reiji the most.