First of all, society puts way to much emphasis on sex, it's fucking ridiculous. You're only 18. You have sooooooooo many years ahead of you for all of that. Trust me, coming from a girl, right now at this point in your life they are either:
a) a distraction or b) trouble

It's completely normal to want to be with someone. Just chill. Besides, if you start having sex with girls you are not married to you run a huge risk of disease or impregnation. Those are the last things you need to deal with right now. Just get through school, date if you like, but it should not be your main focus. After you are done with the school thing and are financially established then you can put more of your time and energy into a relationship. Trust me, you will be much happier.