Are the two of you actually a couple? Or do you just like him and think he likes you? And did your friend start liking him at the same time you did.
Because if he is single and your friend liked him around the same time you started to try for him then she has done nothing wrong as you have no more claim over him than she does. There is nothing wrong with you both fighting for him but don't resent your friend if this guy chooses her over you.
However if you and this guy are a couple and she is trying to steal him from you then what she is doing is very wrong. You can fight for him if you like but if this a guy who will potentially leave or possibly cheat on you when another girl tries for him then he really isn't worth fighting for.
