"Dear Diary, yanderes do exist. My boyfriend was one."

Marc did not expect to save the school from a bomb his senior year. It all started when he fell in love with Dupont's bad boy, Nathaniel Kurtzberg, and they became the Bonnie and Clyde of the school. They've poisoned Chloe Burgeois, the mythic bitch, shot Lé Chêin Kim, the MVP, and stabbed Lila Rossi, the serial liar. All three have hurt Marc in some way.

And for each of them, the duo made their deaths look like suicides complete with fake suicide notes, curtesy of Marc's ability to forge handwriting

He had let it all slide, but recently, Nathaniel's been killing people just for looking at Marc the wrong way or even just touching him. And he's been very possessive even around the nicest people, or those who were already in a relationship.

Marc eventually broke up with him after he caught him trying to poison Marinette Dupain-Cheng, his best friend, but the redhead couldn't accept that. He gave this spiel about how he was doing this for all him, their love was God, and how they could start and finish wars, but Marc was having none of it.

Somehow Nathaniel saw the school as the problem and decided to kill everyone. The students, the teachers, and then he would have Marc all to himself. He placed bombs under the gym where all of the students were gathered, but fortunately, Marc came just in time to stop him... By shooting him.

...

The bomb was disarmed, and now his ex-boyfriend was dead

"Marc!"

Or not

Marc turned to see Nathaniel standing at the school entrance, holding a remote. He opened his jacket to reveal a bomb strapped to his chest. Thinking that Nathaniel planned to kill them both, Marc started to back away until he said

"I'm sorry... You were right. I'm sick. I'm demented... I'm damaged... Before you, I saw love as some joke, but you made me understand... I couldn't lose you. I couldn't let anyone hurt you. If they did, I had to do something... But now I'm hurting you." He's crying at this point, and so is Marc "I'm the problem..." He tosses the remote to him "I started this... I want you to end it."

"Nath-"

"Do it for me. I've hurt you and everyone else enough..."

"... I love you..."

"... I love you t-"

He didn't finish