Hi, Honestly, when I was young (teens-20's) I would definitely tend to "slip into" a character I really liked in, say, a movie. That subsided over the years, really.
Sometimes people who are diagnosed with Borderline Personality Disorder take on others' personalities/identities because of the terrible emptiness and lack of Self Borderlines feel. That said, I am in NO way indicating that you have BPD!!
Truly, although I have no idea of what you're "about" as far as medical history and such, it sounds like you're a pretty typical young person. What concerns me, actually, is how stressed you sound and that you sound kind of exhausted.