Willing to divorce my husband

My husband married me in the year 2015 2nd feb and the next year he married another woman on 21stjan 2016 without my knowledge. We are medical students i am a bhms and he is mbbs and also my cousin. So we were not staying then as we were students. I found out now that he is living with the other girl and when i said to leave me he is not Willing to divorce me. Now what i should do please help.