I don't see anything wrong with sex before marriage. So what if they aren't "the one"? Some people go through 80 years without finding "the one".
I compartmentalise a lot of things in life. Sex and love are two of them. It is possible for me to love someone without the sex, but equally it is possible for me to have sex with someone without loving them. I do have morals, they just differ from yours. I am not doing immoral things either as it is natural and I am human.
I think the only truly immoral things that one can do with regards to sex are: cheat on a partner/husband/wife, sexually abuse someone or have the intent to sexually abuse someone (grooming).