Pre marital sex

da

I have see on here a lot of people saying sex before marriage is not a sin or not going to send you to hell. I want to know the verses you base that belief on? Everywhere i read in the bibe say it is sin and un repented sin separates us from God, sending us to hell. I am not trying to call anyone out. i just don't understand how you can as a christan say it is ok.