Marriage isn't all about sex because no lady can have it all. What I prefer is a responsible girl who is hard working and open minded. Sex should be considered after all these. This is because you might see a good girl who is a wife material but doesn't have much appetite for sex or cannot last long on bed. You have to tolerate and be satisfied that way because sex is not the ultimate.
The world is taking sex too serious nowadays, and you will see teens and adults looking forward for sex in a relationship that wouldn't lead to marriage. The reason why sex before marriage is not advisable is to avoid giving birth out of wedlock which is a taboo in some traditions down here in my country.