Is this friendship worth it?

I have a friend - we are (were?) very good friends. She decided to be friends again with someone who hurt her multiply times and who hates me. I can't compete with this person, no matter what I do, even though I've done way more for her than he has. Over the past few weeks, she has ignored me while patching things up with him and only yesterday told me that she is friends with him. I am basically numb since she is my only friend and I don't know what to do any longer. Her and I use to hang out 5 to 6 days a week, but now it's only once every few weeks. I just don't know if the friendship is worth it any longer. Any ideas on what I should do or say to her? I really need help!