When my mother found out I was very lonely, she sent me to a new school. There, I (14F) met my best friend (14F). We really hit it off.
I was pretty ugly so dating was new to me (by that time, 15F). So I dated this guy (16M) who was my first kiss. I got tired of him and I kindly called it quits. I had to keep seeing him because we had English classes together.
He kept texting me. I didn't want to talk to him, neither to break his heart. Once, he even sent a 10 minute recording of him crying. I ended up not being able to feel anything for him.
One month after our breakup, I met another guy. I had planned to tell him about my new boyfriend (which is not completely necessary, although the less asshole option) the next time I saw him, but before that he saw a pic of us kissing.
Again, he sent recordings and pictures of him crying. I put on with this for some days, but then I saw he was too toxic. But due to my personality, I couldn't get rid of him. So I gave him my best friend's(15F) number, as she had a history of dealing with stupid guys (which she did in a fantastic way). Now, I know it was very stupid of me.
I expected her to get rid of him for me, but I know how I was and why I did it, so I excuse myself.
Now, this guy approached me after class and told me he wanted to date my friend and asked for my permission. My friend had led me to believe (and I may be wrong here, because you know, that's what I wanted to believe) she just wanted to play with him.
Six months later, in her birthday, we were having a good time when my ex showed up. I could barely breathe. I left early.
School started and I didn't feel the same magic between us. I didn't want to acknowledge it. On the other hand, she would give me hints about she wanting to kiss me.
So I decided to make a move on her and invited her to hang out (we barely hung out outside of school). At the time of our meeting, she sent me a recording. Laughing the whole time. "He passed by my house, now we are going to his place". I felt like she had played on me. She hurted me so deeply.
I did some research in social media. They had been dating for seven months.
When I saw her in school, looking at her face hurted. I didn't talk to her.
She used this to leave our group because she knew we disliked her boyfriend. She grabbed her stuff and left. I thought "I hope he is enough for you now". I was so sad I went to the toilet to cry. One of our friends came after me and said my ex best friend would come back when they broke up. 
She did. One year later, she apologized. I'm not going to trust her again.
We hung out with some friends some weeks ago. We got drunk and she shared intimate details of their past relationship.
Though I'm cool with how she lives her life (and it's not like my opinion matters), I can't be friends with her, it makes me uncomfortable. Let alone have some kind of affair, which I know she wants. There is a huge experience gap.