First of all, I think you sound far too young to be thinking of marriage and conversion.
Second, it DOES sound to me like you are pressuring her excessively about keeping "sexy promises". Stop being mad that she didn't keep her promise. A girl has the right to change her mind with regards to any level of sexual behavior, and shouldn't have to tolerate a boy whining and pouting about it.
Lastly, I think you should prepare yourself for the possibility she may prefer to pursue a relationship with the other boy. Especially if he is Muslim.
Relax... I'll need some information first. Just the basic facts - can you show me where it hurts?