my friend feels left out? ?

lately my friend has been acting very distant from me and today we got into a little bit of a fight and she told me that she feels left out. We have had the same friend group of 3 people for 4 years now. me and the other friend in our group have cheerleading together, lots of classes together, and we live really close so we see eachother a lot. Now my friend that is feeling left out doesn’t have any classes with me, and lives a little farther away so we only hangout on the weekends. so i can understand why she is feeling left out, but the way she said it to me was in a super rude way and for almost a month now i have felt her feel almost jealous of me and my other friends friendship. she doesn’t treat us the same she is cold and distant. i have been so busy with sports and school but i am never mean to her. i am the most loyal to my friends and i treat them with so much respect. for the 4 years that we have been friends, i have only gotten into at least like 2 fights with her and we made up very quickly after. i don’t know why she all the sudden makes me seem like the bad person when she doesn’t even put effort into our friendship. i get that she feels left out and i told her that i am sorry and that i won’t let her feel like that but there is only so much that i can say or do. i love her but she is just being mean all of the sudden and i’m not sure what to do? we are in highschool (10th grade)