Who will you choose? your bestfriend (girl), or the one you love which is also your bestfriend?.. pls.hlp me..?

I have my best friend(girl), and she is really good, she has all my trust, but when she discovered that I love my another best friend,.. for the first time, she cried, and I don't know why.. She and my another best friend (guy) had a relationship and I am the reason why they had it.. Even if I really got HURT, I don't tell it, just smile and hide what I really feel,. it's too hard to choose, after they broke up, i am also the reason why they did it, coz it looks like he has chosen me,:P now, he's courting me, i don't know if it's right or wrong.. help pls, need many advice!,, pls.