Exactly why is it sin to own intimate relations aided by the girl you wish to marry?

Just why is it sin to own sex with a lady before wedding, her and want to marry her? God loves me and her anyway and we love Him, too if you love. We pray together and now we want to marry in about a 12 months, because we have now no possibility, exactly why is it incorrect whenever we love one another? An earlier or a year later, is there any difference for god,…