yes, because you only have to do it with the one you truly love and that you're sure that s/he's the one who you will marry in the future. the only problem is, in a relationship, there are so many uncertainties that eventhough you think that you're sure s/he's the one, you end up falling apart. so it's better to have sex after you get married.. at least you won't have sinned when you do that in the right time.