All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
For an Islamic marriage to be valid, some conditions should be met; the most important of which are the presence of the guardian of the wife and two witnesses. So if at the time of your marriage to him you were a woman of the people of the book and the marriage met the required conditions for a correct marriage, then you are considered the wife of this man. It does not matter whether this marriage was called a civil marriage or something else. However, if you were an atheist or not following a revealed religion when you got married, or that one of the conditions for a correct marriage was not met, then the marriage is void and you are not considered his wife.
If we suppose that this marriage was correct, then he is not religiously required to inform you about his marriage to a second wife or inform her of his marriage to you. Since he got married to a second wife, then we think that you should not preoccupy yourself by thinking about it as it could lead (you) to unpleasant consequences. There is no harm in your continuing to live with him and it is an obligation on you to obey him when he calls you to bed unless you are harmed by that (having sexual intercourse with him).
It is an obligation on him to be just between you and his second wife according to his ability. Even if his second wife is far away, he still has to fulfil her rights of spending the night with her and spending on her unless she agrees to forego the matter.
Of course, the above applies if your marriage to him was correct otherwise you are not considered his wife and you have to separate from him and not let him have sexual intercourse with you. In this case you can renew your marriage contract with him by fulfilling its religious requirements.
Finally, we advise you to remain steadfast upon your religion and nurture your children according to Islamic principles so that they will be a comfort to your eyes in this world and in the Hereafter.
Allaah knows best.