You've got to be kidding. Scandal is a terrible thing, and again, roundly condemned by scripture. Consider, too, the question of reputation. Suppose, as is fairly likely, your relationship breaks up before marriage. Even flaming liberals can appreciate the charm of innocence-and choose it.
True love is jealous, and rightly so.
This is why good priests are so desperately needed. But make no mistake about it. Anyone who reads the 1994 Catechism, anyone who peruses the messages of the magisterium, in particular the statements of the Holy Father, will be crystal clear that fornication and cohabitation are not only wrong but extremely wrong and fraught with danger. The Church as a human organization is subject to tides of public opinion. It craves human respect.