What should I do??

I had my ups and downs with couple of friends so I introduced a close friend (Mia) to expand our group. At one point, I had enough with the group and told Mia on how the group bulled/isolated me. Mia told me not to worry about them and that she'd be there for me no matter what, only to find out that month later, Mia's arranging parties with the entire group without me.