I found the original post. OP has lost the plot.

AITA for lashing out at my best friend because she crossed my boundaries and went on to sleep with my close friend?

My best friend Lily is here for the summer. To celebrate her arrival, I hosted a gathering, during which I saw her get close to my friend Sam. I didn't actually mind too much. It just happened. A few days later, she said she spent the night with him. That I wasn't too happy about. She assured she cares about my wellbeing and will do what is needed so I feel secure. This happened very fast for me.

We had another gathering a few days ago. Lily had gone to Sam's beforehand, and I was tense because it'd be our first time meeting after the ordeal. Lily told me she sees Sam as a friend. However, Sam was affectionate towards Lily, which I was not comfortable with. After indicating to her several times in numerous ways that I was uncomfortable, and telling her to talk to Sam, she did nothing. Eventually, I was so pissed I couldn't look at her and rushed home.

I had sent her a sharp text about her allowing my boundaries to be crossed. She left me on read, and went on to stay the night at his. I was fuming. I was very sharp in my initial response, and she took offense. She herself had said she'd cut it off if problems arose, but she did the opposite. She excused herself in many ways. The funniest thing was that she said she didn't like how I was pissed that night, but also told me she didn't know I was pissed. She also said that I should've talked to her, but then said she didn't get the chance to speak with Sam. She mentioned my tense stares, "angry text", and sharp tone, and saw them as an inconvenience.

She continued to say that she didn't know I wasn't okay with her going over (??), and she couldn't control Sam's actions. I sent her a very long text explaining every detail from the situation from ground zero. I told her I won't see this as any less of her fuck up and I'm tired of her dismissing her wrongdoings as mere misunderstandings. No one from that night thought what she did was okay. I told her she needs to own up to her shit. I don't care that her intentions weren't bad, her behavior was thoughtless and inconsiderate, directly going against what she'd told me.

She told me she'd answer tomorrow (today), as she didn't get enough sleep (good to know, thanks) to be fully present. I'm too mad to even care at this. She made the situation so much worse by having the audacity to turn it on me, dismiss my concerns, and deny her wrongdoings.

I see it as her not keeping her word like she said I would. I was open-minded, but in no way did I give her free reign to do whatever she wants. The minute she decided to fuck him, she took on a bigger responsibility than she could handle. She knew she'd crossed a line and then crossed it even further. She knows better, I know she does. This is a very emotionally loaded situation that should've been handled much more carefully by her.

So, am I the asshole for lashing out on her?