Certainly not. Living together means that the two people are trying to figure out if they are truly compatible or not before they tie the nuptial knot. One can always decide against the marriage regardless of the time one has been living together. Marriage is a much wider engagement as it involves families, legalities and subsequently children. One should be very clear whom one should like to spend a lifetime of togetherness. Not that one does not have the right to step out of marriage. But it is much more difficult and complicated.
Affectionately,
Alok Da