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.
On one hand, Islam permits the man to marry more than one wife as long as he is able to provide for them and be just amongst them. Allaah says (which means): {Marry women of your choice, two or three, or four but if you fear that you shall not be able to deal justly (with them), then only one.}[4:3]. On the other hand, Islam permits a Muslim man to marry a woman from the people of the book provided she is chaste. However, he is not permitted in principle to marry a woman who does not follow or believe in the revealed books [has no religion]. So if your husband marries a woman of the book, it is not permissible for you to ask him to divorce you, but if he marries a woman other than from the People of the Book, then there are some details about this. If the matter is just a question of contract on a paper and does not consummate the marriage with her, then in this case it in not permissible for you to ask him for divorce. However, if he consummates the marriage with her, then he is an adulterer and therefore there is no harm on you to ask for a divorce, but first you should advise him.
Finally, we draw your attention to the following matters:
1- Getting married in order to obtain citizenship; if this marriage fulfils the conditions of a correct marriage, then it is a correct marriage. The most important conditions are the presence of two witnesses and the guardian of the bride.
2- Divorcing in papers (in the court, etc…); if this takes place by uttering the word divorce it is considered a divorce whether the husband intended it or not. However, if the term divorce is not uttered and it is only a metaphor that is used instead, then divorce does not take place unless there is an intention for it. The same thing applies if the term divorce is only written but not uttered [divorce does not take place unless accompanied by intention], according to the most preponderant opinion of the scholars.
3- Marriage and divorce are great matters in religion, so one should not play with these terms, to an extent that a person gets married just for the sake of citizenship, or divorce in papers just to obtain citizenship as well.
Allaah knows best.