Am I going to die prematurely if I don't change my lifestyle?!

Not as long as you should so if you cut down a little bit exercise and eat healthy you will live a lot longer

Have you ever heard the saying 'your body is your temple'. Well it is, how you treat it is, of course, up to you and no one else.
I assume no one is forcing you to do what you are As long as you realize that with each negative thing you put in or do to your body will result in a negative reaction, now or in the future. In a book The Ten Rules of Life the first and most important rule says "first you get a body, that's it only one" and what you do with it will determine how and for how long you will live with that one body. The rest is up to you.
Seriously though please get help,see a doctor asap and discuss how you feel.......good luck and may God bless you on your journey.

to be honest, it's pretty normal to not wanna cut down on the drinking in your 20's. by the time you're middle aged you'll probably slow down quite a bit, so i wouldn't worry about that. if you do change your diet and exercise you should be fine.

Very possibly, yes..

maybe five year.