How to act around people you know that do not like you?

I never know how to act around these women who do not like me. Most of them do not like me because they tried to be with my boyfriend behind my back and he denied them and warned me that they were not real friends to me like I thought they were. I wish I didn't have to be around them but unfortunately I do. Also they say I'm conceited just because take care of myself and I like to dress nicely. I can't afford much but I dress as nice as I can and keep my hair fixed nice as possible (I do my own hair but it looks like I go to a shop lol). They love to talk behind my back but I don't care about that. I just never know how to act when around them and sometimes they gang up against me and deliberately try to make me feel isolated, out of place and unwelcomed.