I guess I have a somewhat differing opinion on this...what benefit would your parents gain by knowing now vs. what possible outcomes could happen.

You have concerns of no place to go...when do you turn 18? When 18 will you be done with high school? Do you have a job? Would it support you getting an efficiency apt or living with a friend?

Prepare for the worst and hope for the best...so I guess my answer is what just a little longer so if the worst does happen you are in a better position to fend for yourself.

This may seem against my normal advice of having a candid sit down conversation...however...part of that is picking the right time. Maybe the right time is when you can answer the questions from above...