Who killed Y/N Stark?

Chapter 3 - Tape 1 Side B (Natasha)

"Next up we have Natasha. You were a huge part of my life so therefore you're also a huge part in it ending. You could've helped me, but you were too busy chasing my boyfriend." Natasha and Steve look at each other for a fleeting moment as the tape continues "Don't get me wrong you helped me a lot. But when I really needed you, you stabbed me in the back. You knew I started dating Steve after the Wanda situation. Didn't you? I mean you were heavily involved in the Wanda situation seeing as you were my original rebound." At this point Steve looks back to Natasha as everyone except Wanda seems shocked by this news.

"This won't mean anything right?" Natasha asks.

"Nothing at all." Y/N agrees. 

"Come through here." Natasha smiles grabbing her hand pulling her into a small room.

"What are we doing in here?" Y/N asks, looking around the room.

"Exactly what you wanted." Natasha smirks as she pulls Y/N towards her.

"And what is it I want?" Y/N smirks placing one hand on Natasha's cheek. 

"This." Natasha breathes out before kissing Y/N gently.

"I let Wanda believe you didn't know about us so you didn't look like you betrayed her. Then you betrayed me by kissing Steve. So my goodbye to you is... I hope you rot in hell." Y/N's voice eventually cuts out as the tape ends. Natasha's hands fly to her face as she feels the tears finally spill from her eyes while Steve looks down not making eye contact with anyone. 

"So... How long were you two having an affair?" Thor looks between the two.

"It was nothing." Natasha lies.

"That tape suggests otherwise." Thor shakes his head.

"Leave it." Loki tells him.

"Did you know?" Thor turns to him, shocked.

"Yeah." Loki nods.

"And you didn't say anything?" Thor asks.

"It was Y/N's story to tell." Loki shakes his head.

"I could've helped her if I knew." Thor sighs.

"You would've known if you took two minutes to listen to her." Loki tells him.

"What's that supposed to mean?" Thor asks.

"Enough. There's more to listen to." Carol snaps as she presses play on the next tape.