I am a muslim in love with a christian Girl who is in love with my muslim best friend.?

[Lyana]

First of all, Salaam.
Second, THIS (this right here) is why Allah does not want young men and women to be "intimate friends" (as in best friends). You should get your mind away from this, and every other girl, and focus on your studies and your Deen. Bring yourself closer to Allah and He will guide you to your righteous spouse.
If you are having trouble forgetting her, do some Sunnah fasts and extra prayers.
You ARE too young to think about marriage, as you have not completed your studies yet! How would you support a wife and the eventual children?
Get your head away from the girls and become the best Muslim Man you can be, so you will be worthy of finding a wife worthy of you and you two can lead each other to Jannah.
MaSalaama.