Im losing a close friend. what should i do?

i was in a clique of 5 girls who were my best friends about a month ago. two of them (one of which was my absolute closest friend since about 2 years ago) have recently dropped me and basically they broke up with me. one of the other girls has still stayed by my side in & out of school even though the other two only talked to me out of school. But just this past week, she's been ditching me a lot to hang out with the other girls. she hasnt been answering my texts or IMs or anything and shes only been talking to me in school when she had to. sometimes i think shes trying to get away from me and other times i feel like im just being paranoid. should i ask her if shes mad at me or something or should i just let it go and act like everythings fine? i dont want her mad at me or anything because i really dont wanna lose her too.