When you and your friend likes the same person?

me and my friend like the same person and i have liked and known him since i was about 4 and she just meet him and knew him for about 6 hours and liked him she knew i liked him for how long and she. she thinks she has the right to date him.? i understand wheres she coming from but wouldnt a good friend know how long i liked him and not tell me she wont be my friend if i date him ?