N.H. Rev. Stat. § 458:12
If the petitionee is insane and has no legal guardian other than the spouse, the court may appoint a guardian to appear for and answer for the petitionee. Although the insanity of the petitionee may be considered by the court in determining whether a divorce should be granted, such insanity shall not constitute a defense to a petition for divorce. Where a decree of divorce has been entered and where it has been proven by competent medical testimony at the divorce hearing that the petitionee was incurably insane at the time the petition for divorce was filed, the decree shall in no way relieve a spouse from any obligation imposed by law as a result of marriage to support the incurably insane spouse.
RSA 458:12
RS 148:8. CS 157:8. GS 163:7. GL 182:7. PS 175:10. PL 287 :10. RL 339:10. RSA 458:12. 1971, 445:2. 1996, 32:2. 2004, 114:2, eff. May 17, 2004.