Is emotional abuse even possible from an online friend?

This girl and I were on-again, off-again friends for about 5-ish years. This time, it's definitely off again for good, and I do not plan to ever speak to her again. I'm having a really difficult time fully getting past the situation, though.

We met on Tumblr when we were both 12 (almost 13), and quickly became best friends. Even this early on in our friendship, there were clear red flags I feel like I should've seen. She was very volatile. If I said anything wrong, she'd say she hated me, block me, and then unblock and text me the next day as if nothing happened. I think part of me believed she'd grow out of this over the years, but it honestly only got worse.

I started arguing back more frequently, which led to very heated arguments. These arguments could last anywhere between 5 minutes and over an hour; it just depended on when she decided it was over and would block me. When we argued, she would berate me, act like I was stupid, insult me, and tell me she hated me. These things weren't limited to arguments, but when she said them outside of arguments, it was very casual and playful to the point where I just accepted it as being okay because we were so close.

We would get in fights where I thought it would be the end of our friendship forever, and my hands would get shaky, and I would feel sick. Then she'd unblock me, and I'd be okay again. This cycle was very normal to me. Sometimes, after she unblocked me, we would acknowledge the fight; sometimes, we wouldn't. My friends started to notice this pattern and began telling me that she wasn't good for me, and I agreed to an extent.

One of the things that confuses me the most, though, is that she apologized a lot of the time. She would say, "Yeah, I was being ridiculous, that's my bad," or something like that after a fight, and we would move on. She acknowledged that she treated me poorly most of the time. She so often told me that she understood why my friends didn't like her, because if one of her friends had a friend like her, she'd hate them too. She seemed so in touch with her actions and her emotions, and this is why I feel like I'm playing the victim or something. She admitted that she had anger issues, that she lied a lot, that she started fights when she was bored, that she gaslit me for fun, and a bunch of other stuff I'm forgetting.

It makes me feel like such an idiot for staying in that friendship when everyone (including her) said she was no good. But I felt like no one else truly understood her the way I did. She had a rough life, and it made sense to me why she acted that way. I felt like my friends weren't seeing the good side of her that I saw, and that she was just being too hard on herself. In both of those scenarios, I always felt like it was my fault. I thought I didn't tell my friends enough of the good, and I only told them the bad. And I thought that with her, we were both equally bad to each other.

I still wouldn't say I was a perfect friend to her by any means. When she said, "I hate you," I was quick to respond with, "I hate you too," and I think I blocked her once for a few minutes to be petty. Towards the end of our friendship, I started lying to her like crazy by just telling her what I knew she wanted to hear to avoid arguments. When we argued, it was definitely two-sided. There's more, I'm sure, but the moral of the story is that I was not the best possible friend to her.

When I think about that, I feel like I'm being too harsh on her. I feel like the things she did to me were much more frequent and much more cruel, but I'm obviously biased towards myself.

I just feel like I'm going crazy. It's been a little over a year since we stopped talking, and I still have nights where I can't sleep because I am so paranoid she'll find some way to text me.

I can give examples of things she said or did if needed, I just feel so ridiculous for being this affected by an online friendship. Thanks.