Possessive friend(?)

Before I start, I have cut ties with her and no longer friends, I just wanted to rant. So, I am an introvert, I've never been the one who approach a person to be friends it's always someone approaching me and asked if we could be friends and I usually just agree. In middle school, three girls approached me and asked to be friends. I agreed but ended being friends with only one of them, Magpiety. At first everything's fine. But I noticed everytime I 'prioritized' someone over her, she got upset and ignore me. For example, someone else was talking to me in class, suddenly she spoke to me and I gently, kindly, told her that this other person is talking, wait your turn. But she didn't like that and literally ignored me for the rest of the school day. She would get upset too if I get up from my seat to talk to my other friends. She also get upset when I 'ignored' her. She'd talk to me suddenly, but I was on my phone and didn't notice. When I noticed I immediately apologize, turn off my phone and asked her to repeat what she's saying. She never want to. She'll just huff, cross her arms, faced the other way and ignore me for the rest of the school day.