You are still young and there is no rush. Why rush into something with someone you have reservations about. Sex is not going anywhere, it's been here forever. Why don't you do rewarding things for yourself like get a college degree, lose weight, volunteer to help homeless instead of worrying about a sex life with someone you have doubts about. You don't need to get married now. Why don't you wait until you get about 30. That way you will be mature enough to make obviously better decisions than what you have been making so far.