My best friend has a new guy friend and I feel so left out what should i do?

Im a girl and I have been best friends with this girl for 10 years. Were both 21 and we always hang out together travel together we do everything together were kind of like sisters were so close but she started hanging out with this guy and i feel left out alot she says there just friends but am i wrong to feel left out and traded in it hurts alot and sometimes makes me cry. she started hanging with this guy more in the past month so it hasnt been long