You sound like a very upstanding young man who has great concern for others. It is a very difficult situation that you are in. Legally the best thing for you to do is to keep the relationship as a friend ship until such time as she turns 18. I would make sure that you two are always in a group and never alone for anyone to be able to accuse you of any wrong doing. Her parents may react in a way that you do not expect given the age difference and that could cause you great grief. Given that you are 18 and she is a minor any accusation or conviction of even a small offense may result in your having to register as a sex offender the rest of your life. Good luck.