Aniruddh & Bondita are still married to each other lawfully. There were no divorce papers signed & also that ulta phera cannot break a marriage. A marriage also cannot break by just saying.
Also the child marriage law is a retrospective law. It cannot break previously annulled marriages. Also in the recent episodes, the makers have stated through Bihari that ulte phere cannot break a marriage hence Aniruddh & Bondita are still husband & wife when it comes to law.