It is a sad situation. A marriage that once held hope for a couple has dissolved and a new relationship has emerged before the difficulties that beset the first were fully resolved. Do the parties to the marriage and the affair have a responsibility to resolve the outstanding issues before moving on?
This question was addressed to the Responsa committee of the CCAR (the Reform Movement's rabbinical organization) in 1986. The specific question asked if the rabbi who has received such a request should perform the wedding ceremony. The full responsa can be found at http://data.ccarnet.org/cgi-bin/respdisp.pl?file=192&year=carr .
The answer notes two sides to the question.
On one hand, there is a clear prohibition in classic sources on a marriage between an adulterer and their lover – regardless of whether the adulterer is male or female. The sources go on to note that a woman who commits adultery may not subsequently remarry her husband nor may she marry her lover, even after the death of her husband. These sources underscore the sacred nature of a marriage and refuse to acknowledge any legitimate union coming from a betrayal of that bond.
On the other hand, the sources recognize that there are times when a marriage takes place despite their disapproval. In that case the sources affirm the marriage as valid. There is no benefit in censuring or punishing the couple. After all, it is now a marriage in fact and one hopes that it may fulfill the hopes of the couple for a loving and sacred relationship.
Our question addresses the situation after the get, the formal divorce decree, has been issued. The unraveling and reweaving of these strands of relationship are complex and may have unexpected consequences. One hopes that the process that led to the divorce agreement included formal counseling and personal soul-searching.