AITB for thinking my friend crossed a boundary I set?
Due to personal reasons, I don't have much capacity right now to listen to my friends vent about their own problems.
My online friend, A, frequently messages me to talk about their problems. Even if I don't reply to their messages because I'm busy, they'll continue to type paragraphs as if they're writing in a journal. They're not the only friend who vents to me, but they're definitely the one who does it the most, and it gets pretty emotionally exhausting.
I tried to set a boundary with A about this because I opened my messages to another series of paragraphs about their problems, and it was just too overwhelming. I explained this to them, and asked that they please ask me first if it's okay to vent to me. At first A tried to push back, saying they're not necessarily asking for my advice or help. I explained why that didn't really change how it made me feel, they said 'Okay'.
The following day, A messaged me saying they wanted to talk about something, but that they would blur the paragraph as a spoiler so I wouldn't have to read it, and proceeded to do so. This felt like a breach of the boundary that I'd set the day prior, as regardless of when or if I read it, I'm still aware that they're sharing their problems with me. I explained this to A, and asked that they please respect the boundary I had set.
A did not like this. They said I was accusing them of being intentionally disrespectful and that I needed to 'stop acting like [they] intentionally crossed a boundary', and told me that I was too vague when I communicated my boundary the day before. They argued that they weren't venting, just 'updating' me, and they started picking apart the definition of venting. They then said that because I'd mentioned previously that all those paragraphs were too much, they interpreted that to mean the paragraphs would be fine if they were blurred out, and that I should have been clearer, and that they 'won't be spoken to like this'.
The whole thing felt really 0-100 and weirdly defensive. I've set the same boundary with other friends recently too, which A is fully aware of (ETA: nobody else had an issue with it. I told A it wasn't just them when I set the initial boundary). I'd tried be as polite as I could in restating the boundary and explaining why to try and avoid further misinterpretation, and looking back it was probably more explanation than I needed to give.
I was so distressed because A was making me feel so guilty and unreasonable for what I'd thought was a pretty normal boundary, to the point that my heart was beating out of my chest and I felt physically sick. I ended up saying I was done, and blocking A. I didn't feel like I could really try to defend myself in the moment.
I didn't sleep last night and I've been on edge from constantly second-guessing myself about all this all day. AITB for feeling that they had crossed the boundary I'd set, and for asking them to please respect it?