depends on your beliefs. you are supose to wait until marriage, at least that's how i was raised. you aren't anything offical just because he proposed.
you can have sex whenever you think is right for you. But if your religious and believe in the sanctity of marriage you mine as well wait. Its always good to "test drive" and make sure that person is right for you before you tie the knot.
that would really depend on your religion.
depending on that though, christians aren't really supposed to have sex until after they're married. but no body i know that's a christian followed that rule.
you have to test drive the car before you buy it