In Scripture we see liberty of religious vows made before conversion, and even illicit marriage is called marriage, as is any taking of a wife, even when it was under conditions that allow for possible annulment. But as Rome provides many conditions, then as said, thus multitudes of RCs may be living in fornication seeing at others like them have received annulments (though i do not doubt many Christians are living in adultery).
However, your charge that the life long marriage btwn two never married adults is no better than homosexual marriage, all rests upon your premise that Rome has supreme authority (and your interpretation of this event, as other RCs disagree or see it as adultery), but as we see this as being that of self declaration, your assertions simply have no weight.
They took vows. The vows precluded marriage. They "married" anyway. That is fornication.