Just be clear, make sure you have the consent of the Arabs first wife and children , because this is a very common situation here and the second wife usually bears the brunt if the first wife comes to know, so be sure about this.
Regarding marriage, if you intend to get married on mosque, get converted to Muslim first and then the rest your boy friend will figure just by asking around, make sure this is not the reason he gives to delay this marriage,

Gud luck , think before you fall into a trap