A very toxic friend which ruined my social life, and how i dealt with him

[Dessehead]

This might be a VERY LONG topic

Back when i was in my seventh grade, i was sitting next to a guy who was not that popular in school, just like me. Let's call him Mark. We weren't talking that much in the beginning, but as time passed, we managed to find topics we could discuss. He was one of those guys who could make you laugh, who was interesting but not so thoughtful. We were hanging out frequently. Not a single day passed without us greeting each other or sharing a bottle of Pepsi. After a few months, problems began to arise. I realized that i was spending too much time with him, and because of that, my grades started to drop. My parents were very worried about it, so they warned me to be a bit more careful with my time. They also got a chance to meet him on several ocassions, they said that he was not a very good friend to begin with, but i ignored them, thinking that i could help the guy iron out some of his flaws before High School. Fast forward two years later: We started going to Highschool, and with that, new people emerged. At first, nobody gave a damn about me. But later, people started making fun of me for being  "Way too different" than others. Mark jumped between me and them, saying that my character is good as it is. I felt that he was a Godsend, ready to help me pass through the remaining years of pain. I thought that this friendship was going to help me fit in with others.
But not in an obvious way.
From the same class, i met a guy who was listening to metal, Stephen. Being my favorite genre of music, we quickly found topics to discuss. He decided to invite me to a very well known underground place. Only i could attend, (Mark had a rare chance to hang out in the city, because he lived in a village 8KM away from it.) so i promised Mark to bring him in next time. I went there and managed to leave quite an impression to others, being a bit socially awkward (Which didn't bother them at all.). I also had fun talking to a guy, let's call him Daryl. All of us were enjoying, going to concerts, having fun and popping a cold one in the bar (Mark was also with us)They even decided to surprise me for my birthday, by giving me cash and gifts.. I finally felt accepted by others, for the first time in my life.
Untill, this happened.
One night, in front of a concert hall (The main door, where the tickets were sold), i was chilling out with a beer in my hand, until Daryl walked up to me and said "What shit did you talk about me, punk?", i was confused as hell. I said to him that it must've been a mistake, and that i didn't tell shit about him. He was angry as all hell, he sighed and gave me that look. Like he was going to rip me to shreds if he heard another thing. I told Mark about what happened, he said that the guy was jealous of me, and that it's not a big deal. Several months later, Daryl was constantly making jokes about me. I decided to be a bit more brutal, and make fun of his style. It didn't get received rather well and he turned hostile. Next day in school, i realized that i was a jerk to him, so i decided to call Mark and tell him to invite Daryl to coffee after school, as an apology. Mark returned after several minutes. He said that Daryl wanted me to go and apologize to him in front of the whole group.  I gathered my balls and walked up them, Daryl reacted furiously and told me to "Fuck off with my excuses". I felt helpless, humiliated and lost. On that very same day, i saw my ex hugging with a guy ten years older than me.
I couldn't take it anymore.
I went to a newly built bridge, climbed on the guardrail and was ready to take my own life. I decided to call Mark, to say goodbye. He answered and told me to wait. He started telling me that i was a special kind of guy, who can't be understood by primitive jackasses. The very next day, we went to a coffee and he made me feel better. "Even though others are against you, i'll always be by your side."
Fast forward to 2017, we graduated highschool. I was dating a girl which i really loved. The first two weeks of our relationship were magical, until she went to a different town to see with her sister. She returned with tears in her eyes, saying that she heard awful stuff about me. We managed to track down the source of all the contradicting information.
It was Mark.
Long story short, the fuc**r was turning everyone against me so he could look cooler in front of others. He was behind all of the social problems and complications i've had since the very beginning. I decided to cut him off from my life, completely.
Several months later, one of my colleagues from school decided to call me for a coffee. I accepted and went to the bar, only to find him and Mark sitting at the same table. Mark begged me to help him, saying that no one wanted to hang out with him, that everyone avoided contact. I was leading a battle between the ego and soul inside of me. My ego was screaming: :" Don't help him, he ruined you!" and my soul was telling me: " Show him the way, but don't help him."
I listened to my soul.
We went to a local internet caffee, where i spent two hours, showing him books for self improvement and channels (Actualized is one of them). When we were done, i told him to stay away from me completely.

I managed to fix most of my troubled relationships with people, i just hope that some people will understand that i had no control of it.
So tell me, what were your experiences with toxic people?