Nobody knows why Scarlett got in her car to drive off from a party alone and drunk that night. Well, no one except me. Friends since forever, we grew up next door to each other in a sleepy provincial town on the south coast. Our parents shared the school run, local gossip and Christmas drinks. Our doors were always open to each other and both families knew that where they found one of us, the other would be.

I’m an only child. But with Scarlett living next door, I always say I grew up with a sister. We were very different though, and I often felt in Scarlett’s shadow. People lit up in her presence; they beamed in a way that never happened when I entered a room. She was pretty and charming, a true free spirit. As we got older, she transitioned from a golden child into that girl who all the guys fancy. Where most of us walk through life, Scarlett danced.

Our differences never stopped us being friends – in some ways, we complemented each other perfectly. But when other people were involved, I became invisible.

After years of growing up in each other’s pockets, we went our separate ways for university. I got a place to study at Leeds and Scarlett stayed south, in Bournemouth.

My life changed pretty quickly then. Why? I found drugs. Or maybe they found me. Halls were awash with it all: acid, ketamine, Valium, ‘shrooms... for the first time ever, when I was high or tripping or off my head, I felt great about myself. Ecstasy, in particular, blew my mind. When I was up, I felt like I was Scarlett – one of life’s beautiful people.

i killed my best friend
.

With the drugs came another circle of friends and partying was the glue to our friendship. But as I was deep in this voyage of self-discovery and awe, Scarlett was struggling.

Her dad was very sick with cancer, and she spent most weekends visiting home; she totally missed out on that vital bonding time over Fresher’s Week and beyond. Plus, Bournemouth wasn’t nearly as wild as Leeds, so she did no such hedonistic experimenting. She did have a boyfriend though.

I met him in first year during the Christmas holidays and we chatted incessantly. It was obvious why she loved him so much: Nate was gorgeous – think tumbling blond curls, green eyes and perfectly placed freckles. He was also sweet and really shy, not like Scarlett at all.

Scarlett spent the next six months filling me in on the new love of her life via endless text screenshots and I sent her crazy videos of raves and house parties in return. She hadn't done drugs before; I could sense my new identity made her uneasy, but I didn’t care. It felt good to be the pioneer for once, the one in the spotlight with stories to tell.

Where most of us walk through life, Scarlett danced

When the summer holidays hit, some of my university mates and I decided to head south for a weekend and throw a party in a disused quarry, not far from where my parents lived. Scarlett and I used to go up there as kids, playing games and plotting our futures.

This time it was going to be different. Not only was I up for any excuse to get high, I’d invited a load of local faces from school and couldn’t wait to introduce them to the new me, the one with DJ mates and a stash full of class As.

Scarlett and Nate were pumped for the party too. By this time, it was clear that Scarlett's father was dying and, after all the care she had been giving him, she was in need of a good release.

Word got out about the rave; it was rammed. More than 100 bodies were dancing together, a thumping baseline blaring from a pair of massive speakers.

I’d come prepared. Inside my bum bag were 40 pills, a few hundred pounds worth of coke and endless wraps of K. Behind the decks, I’d stashed hundreds of laughing gas canisters – for the after party. I bought in bulk so I had plenty to share, but to be honest my drug use had spiralled out of control by that stage. I was using alone, self-medicating to stem uncomfortable feelings of inadequacy.

I spotted Nate and Scarlett by the bar: both of them seem wasted. When Nate went to the bathroom, I ambushed him. I could tell he was curious about drugs and I wanted to impress him. Yes okay, I fancied him, and I hoped we could build on the connection we'd made – there's nothing better for that than getting high together. In the back of my mind, I knew that if Nat took drugs, it could create tension between him and Scarlett.

i killed my best friend
.

I offered Nate a pill and he was drunk enough to accept it without question. Then, Scarlett returned and what happened next is blurry. One minute a gang of us – Nate and Scarlett included – were dancing, the next Nate and I were separated from the group. He was rushing hard. I took him out of the area for some fresh air. He lay back on the grass and closed his eyes, dipping in and out of a sketchy sleep.

In that moment it felt like our destiny to be together, so I climbed on top of him and kissed his lips. Suddenly I wasn’t invisible anymore, I was that girl. For a moment, I was Scarlett.

I knew that if Nat took drugs, it could create tension between him and Scarlett

A cry broke the spell. As the real world began to permeate my fantasy world, Scarlett came into vision. She was staring at me in horror, trying to make sense of the scene. I tried to speak but nothing came out (that's ketamine for you). Nate was out cold.

Scarlett reached into her bag, removed her car keys then flung the contents – and her drink – over me. I was too deep in my K-hole to care. When I came to, Nate was gone and police were patrolling the site.

Nobody could have survived the impact, the authorities said. Scarlett had crashed into a tree about a mile from the party. She died instantly. Our families were broken. United in grief, they mourned as one. The pain of being held by her parents as they sobbed is scored into my heart. Her father died soon after.

As the initial shock wore off, questions came thick and fast. ‘Why did she leave the party?’... ’Did anyone see her go?’... ’Why wasn't she with Nate?’ I played dumb. In fact, I made sure to ask the questions too, that way it would seem like I was also looking for answers. Nate and I kept our distance. Despite the fact he was out of it when Scarlett left, I’m certain he could tell something had happened between us. The funeral was horrific. I was paranoid that people could tell we were dodging each other. After that, I never saw him again.

What the f*ck was I doing? I was wasted, but I saw Scarlett grab her keys. I didn’t even try to apologise, let alone stop her leaving.

The five-year anniversary of that night fell this summer, but I’ve never really lived since Scarlett died. My head is a mess of what ifs and whys, and I can’t shake the memory of her face. I dropped out of uni the year after it happened and now live a grey, isolated existence in London – it’s easier to stay anonymous in the city. Somehow, I’ve managed to hold down a reception job at a dental practice: ironic really, as I find it difficult to smile. I guess I’m good at faking it by now.

I'm on a cocktail of drugs (prescription only this time) for anxiety and depression, and, before you ask, yes, I’ve tried therapy. They all said it wasn’t my fault, but they would say that, wouldn’t they? I hate what I did, and I will never forgive myself for what I didn’t do. I’ve thought about ending it all, but I deserve to suffer. Guilt is now my only real friend, and I will never let it down.

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