Attending the janaazah of a Shia

The shia revile the Sahaabah (radhiyallahu anhum) and believe that the Quraan is distorted. People who hold such beliefs are out of the fold of Islaam. It is not permissible to participate in the janaazah of such people. If you had participated in the janaazah, then you have committed a major sin. You should make sincere taubah to Allah Ta'ala for participating in the janaazah salaah and you should make a firm resolve that you will not repeat this in the future. However, your nikaah is still valid.

And Allah Ta'ala (الله تعالى) knows best.