Sweetheart, don't give sex just because you are afraid he will leave you if you do not. You are worth more than that. He should care enough about you to care about your birth control. He should help you get to a doctor and get on the pill, and he should be willing to use a condom. Also, he should love you enough to marry you even if you two don't intend to get married right now -- if he does not, what are you doing sleeping with him without protection?
if you don't want to get pregnant use a condom or get on birthcontrol.
you need to go see a doctor. there is no medicine you can just go take.
are you aware of your options regarding Birth Control Pills? You must see a doctor for them to be prescribed, but unfortunately while they can help prevent pregnancy, unless you are using a pill AND a condom, you still have a chance of getting pregnant. I know it feels better not to use a condom, but you HAVE TO use a condom EVERY TIME or you are running a very high risk of pregnancy. If he loves you, he will understand and agree to continue using a condom every time. There are several options that you can use however if you do not wish to use condoms....there are pills, there is a birth control shot, and there is a plastic or copper device that they can put into your body to help prevent pregnancy for years without needing any follow-up. Please speak to a doctor about your options, they can help you, and it is VERY inexpensive in most countries for birth control. Good luck :)