If one's husband has a vasectomy without even asking the other spouse about it - is this legal grounds for a separation, as now it is not a valid marriage since the couple is not now open to procreation?
The validity of a marriage is determined by the couple's ability to make an honest and well balanced adult decision at the time of the wedding--and not later. The dishonest and sinful behavior of the husband here is a serious matter, but it cannot invalidate the marriage. I don't know enough about the people involved to comment on the advisability of separation.
Fr. Vincent Serpa, O.P.