E and C had a conversation via text the night before, during which C told E my bf was cheating on me. At which point E, who was drunk, told C what had gone on between me and my coworker. 

Now... I couldn't stay pissed at E for very long, after all the entire situation was my own doing. However, I was, and still am EXTREMELY pissed at C. Whether or not S deserved to know about what had happened is beside the point - it's not her business and it wasn't her fucking call to make. I had my reasons for not telling S. I loved him very much, I regretted my decision and shortly after that party I broke up with him. Two days later he and I got back together. I thought maybe I could just put the past away, move on, and have a fresh start. Learn from my shitty decision and be a better person and gf because of it. Guess not... and you know, maybe I didn't deserve a second chance. I wouldn't blame S for hating me. I'm just baffled by the irony. See, S doesn't believe that I truly loved him and that I'm not a terrible person, I'm just a person who made a terrible mistake. He was pissed that I didn't tell him.  Buuuut... he didn't tell me that he had led all his coworkers to believe he and I were in an open relationship. He didn't tell him he had hooked up with one of those coworkers - coworker, by the way, he had a history with. He decided to take the moral high ground and judge me. The both us deserve judgement, I suppose. The thing is, I would have loved if we could've talked about it. That when I confessed he could've confessed too. Maybe we could've worked through, gotten stronger, grown in our love. I would have chosen to forgive and try and understand why he had cheated. I believed him when he said he loved me. And after all we went through together, if he couldn't believe the same of me, maybe our relationship wasn't worth a damn to begin with. I dunno. Maybe we we're both good people, stuck in bad times. Maybe we could've been special and made each other happy, but the circumstances were just wrong. I don't think either of us deserve to be crucified. I just wish he and I could find away to accept what happened and remember each other and the time we had together fondly. 

UPDATE: he didn't run out and cheat after he found out I had. He cheated while we were still just a happy couple. 

ANOTHER UPDATE: I did cheat first. Then broke up. Got back together. He still didn't know. Then he cheated. Then he found out I cheated. Then I found out he did. I'm sorry I didn't piece this story together very well.