i feel terrible (what should i do?)

basically my friend and i went to a new school this year and we hung out alot. fast forward I started making new friends and hanging out with more people and she did the same. she was always with that one friend and I felt left out but i kept quiet. now someone told me that she feels like a ghost, and i don't hang out with her as much anymore. what makes me upset is that she's telling everyone except me. she should have told me that she was feeling this way so we could sort things out. but then again I feel bad cause i haven't noticed that my own friend feels like that because of me. she also said that i'm changing. what should i do?