[quote="grokrc, post:1, topic:327781"]
....is it necessary for me to obtain a decree of nullity from the Church if I wanted to remarry in the future? If it is still necessary then would the fact that she is having an affair be justification to obtain a decree of nullity?
All marriages are considered valid by the Church UNTIL it has been declared null by the Marriage Tribunal.
Some marriages are quickly seen as invalid, such as a Catholic not getting married in the Church (Lack of Form) or a marriage after a divorce without the previous one being first declared null.
An annulment declares that there was never a union made where God bound the couple as one. An annulment is based on information about the couple on the date of their marriage. For example, if one of the couple was not free to marry, then the Tribunal will state the marriage to be null, as God did not unite the couple since one spouse was not free to marry.
What happens in a marriage can cause the couple to seek a civil divorce, but it does not mean the couple was never in a valid marriage. Annulments are not based on events after the marriage - such as an affair.
Please speak with your priest who will help you get the proper forms to submit to the Marriage Tribunal.