Okay, this is what I think. Judging from your writing skills, I think you have the smarts and maturity to get through any program you wish. Nursing school is hard and a lot of work, sure, but it's not impossible. If you pay attention and do the work you'll pass, no problem.
HOWEVER. I think you're struggling with a lot of ambivalence. Ambivalence about growing up, taking charge of your future, being an adult. I had the same problem so I can relate. I was very focused on my friends and boyfriend because it kept me in a holding pattern, it was familiar and it was safe. Going to school, dealing with unpleasant and uncomfortable situations, was scary.
These are normal feelings a lot of people, especially females, deal with. My advice is to keep plugging along. Don't let anyone tell you you're too young or you're "not ready." No one feels ready for huge, life-changing events. You get ready by doing it, not by feeling it.
You do have added pressure of feeling like the role model to your younger siblings. No help from me here - being the oldest in the family can be very stressful for that reason. But I believe you can do this. I have faith in you. Now, you just have faith in yourself.