My best friend and I liked the same guy. She betrayed me. What do I do?

my coworker/best friend and I both like the same guy. At first, she had no interest and told me we would be perfect together. She even set up a lunch date for all of us and I hit it off with the guy right away. She went on vacay the following week, so him and I had lunch a few times and got drinks. He even kissed me and told me I’m his work crush.

when I told my best friend, I thought she would be excited for me. Instead, she got upset and told me she’s developed a crush too. She felt left out that me and him would have lunch without her. After that, I tried to include her in all our plans.

here’s where it gets messy. We both agreed our friendship is more important and both of us should try to just be friends with him. She kept telling me it’s not worth it. Then one night we all went out, she tried to kiss him in front of my face!! She was completely sober. She was flirting with him the whole night and even tried holding hands. He didn't kiss her back of course and told me she was way out of line. Her and I got in an argument after that but I told myself I will give her another chance because she apologized.

we have all gone out since, but she still hasn’t dropped the flirting and jokes beforehand how it’s a “challenge” to her. we got in a huge fight today. I told her I don’t want to hang out with them anymore in a group because it’s very awkward. She told me to stop throwing that night in her face and she doesn’t want to hear my feelings. Should I cut her off? I’m so sad because up until this we have been great friends for several years and never gotten in a fight. I feel so hurt and betrayed she would choose a guy over me.

also, should I explain my side to the guy? I don’t want to be immature but I don’t want him to think I’m mad at him.
My best friend and I liked the same guy. She betrayed me. What do I do?
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