I will add as another thought, that if we are holding people to a commitment that is binding for a lifetime, then we are doing a lousy job of preparing them.  A few premarital counseling meetings with Father and a Pre-Cana weekend, then we turn them loose and expect whatever they picked up from mom and dad's example to sustain them for a lifetime.  Preparation should be similar to that for the other sacrament of service, ordination, or to the process of joining a religious community.  It would involve several years of discernment and education, required spiritual direction during the formation process, and step-wise levels of commitment leading up to the final vows.  The church can then provide continued accompaniment, financial assistance when needed, and counseling to help couples maintain their lifetime commitment.  If the church is unwilling or unable to do this, it might need to recognize as legitimate other forms of civil union...so maybe it is about gays and lesbians, too.