In the Gospel, Jesus said that (unless a marriage is unlawful) anyone who divorces a wife and marries another commits adultery.
According to that, if the first marriage was unlawful, the pair are free to marry again. The Catholic Church, sixty years ago, going on that, began looking seriously at marriages that being unlawful from the start, could be terminated with annulments.
I am not one of the church’s experts trained to carefully examine the evidence in such cases. However, since I must deal with these matters, I have come up with my simple way of looking into “unlawful marriage.)
I think back over the hundreds of marriages at which I have officiated, and I recall that each time I have asked the same question: “Have you come here freely, without reservation, to give yourselves to each other?’
I see this as four necessary conditions for a valid marriage.
1. they had to be physically and mentally free to marry. 2. There had to be no reservation that had to be there, or else. 3. They clould not be so self-centered that they were incapable of giving themselves. 4. It needed to be a commitment to a true marriage.
(Once in Korea I saw a printed invitation to a five-year marriage. The wealthy boys parents allowed him marry his girlfriend for five years before marrying their chosen daughter-in-law.)