Just got the lead in a student movie. I agreed to do it before I knew what it was about, and what my character would do…

I don’t smoke, but I will have to smoke multiple times.
I’m worried that I will like it, and get addicted (and then my father will think he can start again, and my mom will divorce him)

How am I supposed to perform a realistic s** scene (parts covered, but still) when I haven’t had s** yet?

How do I tell the actor opposite me that he will be my first kiss?

Why am I almost 20, and so unexperienced?