When he turns 18 it doesn't matter that you were already dating. Had a prosecutor say something about a case he was working on that says it all," 17 will get you 20". He was talking about a guy who was dating a 17 year old girl while he was 18. They had sex and girls Dad found out. He pressed charges and the guy ended up in jail even though they had been dating for a year. So, let the rules stand as far as going out because you are still young and your parents are worried about you. They may not show it in the best way, but they are trying the best they know how to protect you. A couple years are not that long in the grand scheme of things.
It is nice that he cares for you and looks out for you, but you need time to grow up. There is nothing you can do about your sister not helping. You can however look out for yourself and you own health. Not sure what those issues are, but you need to do all you can to protect yourself so you can remain healthy.