How do I my friend to stop ignoring me when we're around her other friend?

So let's call my friend Toni, and her friend Cyndi. When ever Cyndi is around Toni, Toni always acts like she like's Cyndi better than me. I told Toni this before, she said she was sorry, and tried to stop, but I few days later she started again. Toni always acts different around me when other people are around. Toni always hangs out with Cyndi, like every weekend, online, in school, etc. I never to hang out with Toni alone, and I like it when we're alone, I can talk to her. How do I change my mind, or get her to act different. Or should I just give up and except that she doesn't like me as much as everyone else?