(a) It is a defense to the crime charged under 6 CMC § 1301(a)(3), 6 CMC § 1302(a)(2) or (a)(3), or 6 CMC § 1303(a)(1) that the offender is
(1) mentally incapable; or
(2) married to the person and neither party has filed with the court for a separation, divorce, or dissolution of the marriage.
(b) Except as provided in (a) of this section, in a prosecution under 6 CMC § 1301 or 6 CMC § 1302, it is not a defense that the victim was, at the time of the alleged offense, the legal spouse of the defendant.