I don't know how to deal with the upcoming death of my crush & friend

What do you mean by hallucinate?
Are you hearing voices? seeing things? Or are they just delusional thoughts?
Because those are very different.
Either way I would go see a doctor / psychiatrist.
Schizophrenia usually hits during puberty or in early 20's and can usually be brought on by a lot of stress or traumatic situation. It is passed genetically and sometimes just happens for no cause at all. I can't diagnosis you but google the symptoms and see if its similar. Maybe even talking to someone about it may ease your mind a bit and make you relax.