I am 21 years of old. In my childhood I fell in love with a girl in my neighborhood. Gradually it grew deep involuntarily. She also with me. Both of us pray to God all the time to unite us in both the world. There is no other sins between us. We can't imagine our being separated. But as by the decision of God she married someone else. (I am a student now) Now we are greatly worried. She told me that if we pray and work hard, we can unite in paradise, and live together there through out eternity.
Is this possible she married someone else? We can't forget each other.
I am requesting a detailed answer.

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

The woman in Paradise is the wife of her husband if the latter is in Paradise with her. But if she married two men, she would be with the last of them or with the one of them who had better ethics and better character. So, since this woman has a husband in this life, it would be an aggression to ask Allah to give her in Paradise to another man. Dear brother, be satisfied with what Allah has allotted you and cut all relations with this woman. You should know that all matters are in the Hands of Allah. The affection and inclination you find in yourself towards her as well as the affection and inclination she has towards you are all nothing but Satan's whispers and insinuations.

May Allah protect us and you from Satan and make us all good Muslims.

Allah knows best.