- Shin Hye thinks Hong Ki is cheating on her (she's either insecure/paranoid/mentally I'll)
-Hong Ki is insensible (which means to be unaware, oblivious to) as he is too distracted to notice how she is acting/feeling
- She breaks up with him, but he can't accept it so he waits outside her house (he said this in his interview about the song). The part when she's in the tub is when he leaves, but she imagines be leaves with another girl.
- She realises that all along she was just imagining things, the girl in the photos was her all along
- As for the blood? That's up for interpretation. Perhaps she was sick. Perhaps she was depressed.