@SSJR2, the doctor was thinking (thought bubbles) 'I thought she had another target', so doctor's at least telling the truth about flute girl being a 'witch'
this chapter does show flute girl genuinely likes him, so, I think there are three possibilities:
1. flute girl knows about the disease, but actually didn't know MC has it and just happened to pursue MC starting now (since MC coincidentally saw her masturbating)
or
2. flute girl figures MC will die soon anyways (since his condition was leaked to lots of girls), so she wants him for herself (instead of letting other girls get him)
or
3. doctor isn't completely telling the truth about the disease/how life-threatening it is (though this is unlikely because she was speaking on the phone in chapter 2)
I'm pretty sure the doctor researching his condition suggests it will not turn out like previous cases.