My closest friend let me down.

I have a really dysfunctional friend group. My best friend, E, was briefly involved with one of the guys in our circle, M, but it never became serious. A similar situation occurred with me and another guy in the group, B. I actually fell for B, but things got complicated because he didn’t feel the same way. As time went on, I found myself getting closer to M, although it's purely platonic. Meanwhile, E and B started spending more time together since they live in the same town. M grew jealous of their growing closeness and mentioned he suspected they were more than just friends. I assured him that wasn’t possible; B isn’t even E’s type. Over the weekend, we had a small gathering, and I discovered that B had some inappropriate photos of me—some even taken without my consent. I confided in E and we managed to grab his phone to delete them. The next day, M called to tell me that E and B had kissed during the same gathering. I was skeptical until I asked E directly; she eventually confessed via text that she couldn’t hide her attraction to B any longer and went for it. The betrayal I felt was overwhelming. How could my best friend pursue someone who had hurt me, taken those photos without consent, and who I was still not over? She apologized profusely, but I’m so furious that I can’t even think about having a civil conversation with her. Our five-year friendship feels ruined over a single night. E said, “I wanted to indulge for once in my life,” and claimed she intended to tell me about the kiss right away but never did. I can't shake the feeling that she wouldn't have come clean if I hadn't found out myself. My heart feels shattered, and I’m at a loss for how to move forward.