I have committed sins before marriage. I regret the act now. I always pray to Allah and ask forgiveness. I am married to my cousin who had all the bad habits and he had an illicit child from an English lady. I had a daughter and she died. He was going with another English lady who gave birth to another child of his. Now I have a daughter. She is one month now. My husband went on holiday with his girlfriend and daughter. He knows that I know everything and I tried to say don't do these things, think about your afterlife. But he is not listening to me. What should I do?
I am always reluctant to give specific advice about personal cases, because often I am not aware of all the details.
My following suggestion is based on my understanding of the information that you provided:
If you have already advised your husband and he has rejected your advice then I suggest you threaten him that at the first stage you will going to complain about him to those relatives or friends who while keeping it as a secret may be able to persuade him to stop. Then, if this did not help, at the second stage you will take the case to the court to demand divorce (if you are living under the Muslim law) or to announce divorce (if you are living under the non-Muslim law). However you should only make this threats if you are determined that you will do them, otherwise it will most probably make it worse.
Another solution is to advise your husband to marry that woman as a second wife, however this very much depends on what you feel about it and also whether the law in his country of residence allows this.
I again stress, the above suggestions are based on my understanding of the very limited information that is provided to me. You need to use your own wisdom to decide whether the above suggestions are going to be helpful.
What I can say from religious point of view is that it is not at all advisable to live with some one who is doing Zina.