Assassination Classroom Yandere One-shots!

Can't believe it (Yandere!Reader x Nagisa)

(This is an AU where they are adults)
You always loved Nagisa. You were childhood friends with him. He promised that you both would get married when you got older, but then one of our great friends died in Junior High because of a car crash, Karma Akabane was dead. Because of his death, you grew overprotective of Nagisa. But then, she waltzed into the picture. Kaede Kayano. You hated her guts and wanted her dead. When you were yelling at Nagisa, he glared at you. "What's with that look? Do you really think I'm out of line tonight?" Nagisa nodded. When he went to go use the bathroom, you took his phone. You saw her number, you grinned and texted her
"Hey, Let's meet up at the Warehouse!"
,you sent to her. She sent a reply, "Sure, What Time?", You sent back a simple 9'o Clock. When the clock turned to 8:30, you left to the warehouse and waited. When she arrived, you saw her: You walked up to her and grabbed her, you tied her up and gagged her and put her in the trunk. She struggled as you drove away to your house and put her in your basement. You sat on your bed and stared at your wall that was covered with pictures of Nagisa. You giggled and looked at a picture of you,Nagisa, and Karma all together. There was an unfamiliar face in the picture. Suddenly, the doorbell rang. You went to see who it was. It was Nagisa. You opened the door and let him in, "(Y/N), where's Kayano?", he asked. You blankly stared at him, "not here."
He saw through your lie,"Where is she?", he asked again. You grabbed him and dragged him to the basement. You tied him up and ungagged Kayano. You took out a gun and put it to Kayano's head. "Tell me you love me, and if you lie, this poor girl will have to die", you said. Nagisa's eyes widened.
"Eheh~, Swear that you'll be true and I will let her go right now, just don't lie.", you said. "So what will it be, who do you choose?"
"You! I love you! I love you so much, just please let her go! Don't hurt her!", he said.
"Oh my goodness, I'm so happy to hear you say that! Then I guess, let's get married now! Ok? Tonight!", you said.
"W-what?", nagisa asked.
"You weren't lying, were you? You love me, don't you?", you said.
"B-but...her and I are already married," he said.
No, he was caught up in a lie, her lies. I will cut him free myself. You put your finger on the trigger.
"(Y/N)!! Please Don't! We used to be friends! Remember?!," Kayano screamed. You laughed and pulled the trigger. A bullet shot straight through Kayano's head. She fell limp to the ground, blood pooling around her head. Nagisa screamed and cried.
"Oh quit your crying! Be a man!", you shouted at him, "surely she couldn't mean that much!"
You went up to him and hugged him.
"Won't you tell me that you'll stay? Now that she's not in the way"
He shouted a no to you, and you lost it. You stood up and started walking out but then you turned and shot Nagisa. Then you kept walking.