AITJ for blocking my ex after accidentally sent me a vent message about me?

TL ; DR: My now ex partner has no respect of self or for others. We fought and after they sent me a mean vent about myself... I blocked them.

Throw away account because I don't want to associate this with my profile... I read here but never posted here, so I hope I did this right.

I just really need unbiased insight...
Here is the context...

I’m moving away for university soon, and while reflecting on my relationship, I realized my partner had changed a lot from when we first got together. This was a private relationship, so only a handful of people knew about us dating.

Looking over everything thoroughly, I discovered my partner had become much more immature than when I originally got together with them, and things had become different. Less maturity made me less attracted, for the mature conversation is what made me like them, but I cut them some slack with how they have some mental health issues.

What really bothered me was how they treated others and themselves; they had little to no self-respect and had become so demeaning to friends that some came to me about it and ended up crying.

After some observing, I talked to them, and it led to them being mad at me. They ranted about their friends and made some comments that felt too far at times. The biggest issue happened when they were practically shouting at our mutual friend to the point the people around us were uncomfortable. I know it can be frustrating, but I tried to tell them both to tone it down but left after it wasn't working. My ex partner is fully aware that I seek space when I feel emotional or uncomfortable, yet they later used this against me.

We resolved it and talked more, but this week we had another argument when I brought the friend up for an advice story. They went to vent about how I treated them around others. I validated the feelings, but they somehow misunderstood me and basically showed low expectations about me, and they called me some things. I tend to lightly tease people I care about, and I would’ve genuinely reflected on their concerns if they hadn’t started calling me names and assuming the worst about me.

It could have been a joke, but I took a step back. They once did the same to me when they got upset in the last argument when I said I felt deceived, and they didn't like that. I suppose I could've articulated it better, but it was late, and I just wanted to go to bed.

I got such a long paragraph texted back by morning, and we went on break... but right after, they accidentally sent me a vent about myself meant for someone else. I screenshotted it with much sadness before it was deleted... it complained about everything I communicated on, like we never talked about it, and called me more things...

That ended up leading to an actual breakup because I felt deeply hurt, even though I tried to keep it to myself.

I went to my usuals for advice but also talked to someone who was aware of who I was dating and was biased for my partner. They referred to me as "gross and manipulative" when I expressed my discomfort with how my partner was upsetting our friend by raising their voice at her.

Today I blocked my partner even though we "ended on good terms." I told them I simply didn't want to bother them and I was going through a lot. Though I left my phone number unblocked so they could reach out in the far future long after I left, though I highly doubt it.

It's almost been a week, and now I'm wondering if I overreacted in the second argument. Should I have ignored being called untrue things and not supported my friend being hurt? I've cried a lot, and it's been hurting me because I feel like it's all my fault, that I could've tried harder.

I loved my ex-partner; I adored them! Seeing them hurt people by demeaning and then getting insulted made me worried for when I am moving and this would become distant. Would they treat me like that? Was I obliviously being treated like that?

I'm hurting because it's hard to be like glue and share a friend group, then lose it all over wanting space. Plus, having no one hardly know makes me unable to talk about it, like nothing ever happened...

It's complicated, and I might not have done this justice, plus I am just emotional about it a bit still, but I am open to answering questions if anyone has any.

Never thought to say it but... Am I the jerk? Having that person call me gross and manipulative makes me wonder...

Also posted on r/AmIOverreacting.