Girlfriend Humiliated Boyfriend at Birthday Party He Paid…

I… I don’t even know where to start. I feel sick and angry and I think I’m shaking still. I’m 22M, my girlfriend 21F. We’ve been together a year.
Last weekend was my birthday. I thought it would be a normal night. Dinner, cake, maybe a few friends. I paid for everything. I wanted it to be special. I trusted her to handle her friends. I should have known better.
She invited this guy R. She’s always said he’s “like a brother.” I didn’t like him. Secret messages, weird calls, popping up where he wasn’t invited. I told her. She said I was being paranoid.
But… that night. That night was worse than anything I imagined.
She didn’t sit next to me. She sat next to him. They laughed at memes on her phone. They whispered jokes. Shared food. Every time I tried to talk she said “wait” or “hold on.” I felt invisible. And then… the cake. He fed her the first bite with his hands. Everyone clapped. I just… I just stood there.
I left. Paid the bill. Walked out.
Then messages started coming. Not from her… from my “friends.” Apparently… they had been planning this for MONTHS. To make me look controlling. To make her look cute with him. To record me and laugh. I found group chats. Screenshots. They were joking about how I would react. They literally called it a “fun birthday plan.”
I confronted her. She cried. Said it was “fun” and I “overthink everything.” She admitted she felt “closer emotionally” to him. That I was paranoid.
Then I realized… some of my friends blocked me. Others sided with her and lied to my family. ALL of them. My birthday, the thing I thought would be happy, became the day I realized they were all plotting against me.
I feel… broken. Betrayed. Gaslit. Used. My birthday ruined. I trusted them. I trusted her. And it was all fake.
I don’t even know how to move on. I can’t trust anyone. I can’t… I can’t even.