Most 17 year olds are an emotional mess. You have a lot going on at that age. School, SAT's college applications, possibly in a relationship with someone and don't think you will ever love anyone else. It's a hard and confusing age to be.
I agree with the user above. I think being a teenanger is truly hard , and it's truly hard to deal with our feelings too. However if you're worrying about people leaving, people will leave. BUT the people who are worth it, will stay. You'll grow up and you'll learn which people really deserve a place beside you. Just give it time. Wish you the best of luck