I have been through that type of situations nearly my whole entire life (I'm 17 so it's not much). I was done the same exact thing as your best friends are doing to you. What I learned is that if someone treats you in a way they shouldn't, just walk away, they aren't worth it. I prefered being cofortable with new people and losing my "best" friends rather than every single day trying to stay with them and beeing really stressed out trying to not make them angry or to make them not ignore me. As silenceKills said, try talking to them about it, if they still act like selfish mean creatures I'm sure you will find better friends. If you decide to walk out of the group be aware they are going to get angry, so be strong and good luck.