What if.. she's bipolar. And the "normal" her is her depression while our masking replica is her manic side? So the person herself thinks of the depression as normal and questions any feelings or emotions from when she didn't feel like herself?
There is no way she is dead for real, cause the plot demands a eden sword, they will either revive her or homura will take her place but i guess a human cant do it, and this manga is way more mature than FT, the ruthless way people die or get tortured, i remember when levy got beat up and some other way over the top violence in FT but i guess the concept there was more happy or thats just an effect of a bigger cast
While this is mostly taken from her perspective of things, fact of the matter is, Hiro did love Nagi long before everything that happened, she wasn't toying with him, but rather wanted him to make a move, while at the same time showcasing this possessiveness of him.
Which bore fruit when Nagi and Hiro dated.
However... It was Nagi's feelings for Erika, feelings he likely doesn't have a full confirmation on by the way - that led Hiro to dump him.