No sex before marriage is the standard. But its unfortunate that people dont practice it these days. Anyway to your concern of not going into the wrong woman tomorrow who leaved wayward life and with many health issues that may not allow her have babies later. What i can say in essence is that we all should pray before getting married. As long as a man or woman is your missing rib, then God will surely correct every errors in the past. Thats my input, thanks.