The first time that I passed out on the Chicago L train, I just knew that I was dying from mad cow disease. At least that's what I told my doctor when I was trying to self-diagnose in his office, and he was pretty impressed by the depths of my neurosis. Understand, this was before WebMD when everyone could do it. But he assured me that despite the fact that I had been to Europe and eaten several steaks, I wasn't suffering from mad cow. I had anxiety. And he asked me if there was anything that had happened recently that had been causing stress, and I had to think about the question for a little while. I said, "You know, I haven't been adjusting well to my move to Chicago," and he nodded his head and said, "You know, a transition like that into a new city can cause a lot of stress."

I said, "My father's dying of cancer, and I can't convince him to take better care of himself." He nodded again; this was obviously a story he'd heard a lot of times before. Then I said, "My daughter almost died last year from febrile seizures, and I'm pretty much terrified to be left alone with her." Now this raised his eyebrows. He wrote me a prescription for Xanax and gave me the name of a therapist he wanted me to see right away to delve into this further. Now, I don't know what prompted me to say what I said next, but as he handed me the prescription, I just blurted it out: "There's one more thing: When I was 14 years old, I shot my best friend in the face accidentally, and I watched him die."

Henry was one of seven people to die that day in New York City, 1988. At 14, he wasn't even the youngest – a 12-year-old kid from Queens had that dubious distinction. But his was the death that I saw with my own eyes. The one that I was responsible for with my own hands, and the one I'm going to carry with me for the rest of my life.

Now, home back then was a two-bedroom co-op in the Kensington section of Brooklyn. It was a big source of pride for my mom, who had raised my three older sisters and me almost single-handedly since splitting from my dad when I was four years old. This was the first place that she owned, after what had seemed like an annual ritual of moving. Now, for those who don't know, New York was really violent and dangerous back then. Like Detroit, New Orleans, and Gary, Indiana, rolled-into-one dangerous. You know, 2,000-murders-a-year violent. But I never let the violence swirling around in the world outside ever impact me. I was actually an honour roll student all the way. And when Henry and I met in the seventh grade, we got along immediately. The physical contrast couldn't have been more extreme. He was unusually muscular and well-built for a 12-year-old, and I was just as oddly tall and lanky for a kid the same age. But that's pretty much where our differences ended. We both were into all the same things. We shared all of the same fears. We walked together every day after school to the Carroll Street subway station in south Brooklyn. And we both hated the older boys from John Jay High School nearby, who'd show up every Halloween and rain rotten eggs, D-cell batteries, and of course water balloons filled with Nair on our heads, which gave you a nice surprise when you got home and tried to clean up.

He was my first and best friend. Now on the afternoon of 14 April 1988, Henry and Chris, another friend of mine, came by my apartment like they had many times before. They dropped their book bags and plopped down on my bed. My mother was a captain in the Army Reserves at this time; we had three guns in the house. The .38-caliber revolver was my favourite, not just because it was the one that was kept loaded. It was just the most interesting. It looked like a gun from the movies, and it was the one I always showed to my friends, even though my mom never knew about it. And this day was no different. I started off by emptying the gun, made sure all the bullets were out. Then I demonstrated my index finger spin – the cowboy move that I'd been working on. Then I took a single bullet, pretended to insert it into the cylinder, and pointed the gun at my friends. I can actually remember smiling as I pulled the trigger, ready to shout, "Gotcha!" when I made them jump. But instead of the dull click of a hammer followed by laughter, there was a muzzle flash, an explosion, and shock. Both of my friends, Chris and Henry, had turned their backs to me, and I remember being overcome with confusion. How did the fuckin' bullet get into the chamber?

Chris turned and looked at me, and my heart started racing, and we both looked over at Henry. I guess we were waiting for him to turn around, say, "Oh shit," and then tell me how much trouble I was gonna get into when my mother got home. Now, whenever we're faced with something horrific, I think it's human instinct to want to run, and mentally that's what I did. I just fled into my own psyche. I went back years to being with my father at Coney Island on the pier, trying to catch a bluefish with my piece-of-shit rod and reel, and then the next thing you know, I was back there in the hallway, and it was full of people. My mom was there now, sobbing. The paramedics were there. Of course, the cops were there. When one of the paramedics came out of the apartment, I remember begging him, "Please tell me he's OK, please tell me he's OK," and even though I knew what he was gonna say, I just wasn't prepared for the words. He just said, "He's gone."

That night in the police station I had to recount in detail everything that had happened. I didn't want to. I wanted to crawl under that table and hide. But I did, slowly, methodically, choking back tears when I looked down and realised that my sweatshirt was covered in blood. My dad was there – I almost never saw him at that time – but he was there with my mom, with the same forlorn look on his face. The wake came about a week later, and I didn't think Henry's family would have any interest in me attending, but my mom insisted we go. So when we got to the funeral home, there was a huge crowd gathered around the coffin, and I made my way over to Henry. He looked really nice. They had him in a really nice blue suit. But I remember the coffin making him look so small. And I just stood there and stared at him while everyone else around me wailed. That's when I suddenly heard this woman's voice. She said, "I JUST WANT TO SEE HIM!" and I remember it made me jump, because I didn't know whether she was talking about Henry lying there in a coffin, or me, his killer, standing over him, crying on to his jacket. I knew every eye in the funeral home was on me, and all I could do was just close my eyes and wish that I was someplace else.

Miraculously, Henry's family did not want to press charges. They embraced me and offered their forgiveness, and when the Brooklyn DA hit me with a long list of charges, ranging from manslaughter to assault with a deadly weapon – I think it was 17 charges in total – they were the ones who stood up and said they didn't want to destroy two young lives instead of one. They're the reason that, instead of going to jail, I got one year of counselling. That was my sentence. I remember thanking them profusely outside of the courthouse that day for giving me a second chance when I didn't think I deserved one. In the years that followed, I thought it was odd that no one – none of my friends, none of my family – ever said a single word about Henry. Everyone went about their lives as though he had never existed. The entire incident was wiped from my record when I was 16, so it hadn't even existed in a legal sense, and if I never mentioned it again, it would never come up.

But I thought about it, the shooting and Henry, almost every fuckin' day. And oddly enough, it's what drove me for a number of years. Ask any friend of mine in college; I was the most anal-retentive dude they ever met. I wouldn't touch alcohol. I wouldn't smoke a cigarette. Don't get me wrong, I made up for it years later. But I just felt like I had to do him proud. I had to be perfect. And for a long period of time, I thought I was doing it. Successful career. Faithful husband. Doting father to my daughter, who I watched grow from an infant into a toddler. When my daughter got sick at 18 months, it pretty much derailed all of it. We rushed her to the hospital, her body was convulsing, and all of a sudden all of these emotions and feelings I hadn't felt since I was 14 came rushing back. The feeling of panic, the feeling of helplessness. And that's when it dawned on me, Maybe this is it. Maybe this is gonna be my sentence, that I'm gonna have to see what it's like to lose a child. And, you know, miraculously, she did survive, and the doctor assured me that some children just have a really low tolerance for fever, and it's something that she would almost certainly grow out of. But the damage was done, and when we got back home, everything was just completely different. I was terrified to be left alone with her. I felt like this marked man, and the second it was just me and her, something was gonna go wrong.

It didn't help that after she got sick, a recurring dream I was having about Henry began to repeat itself with disturbing frequency. And it was always the same dream: in the dream I'd be asleep, I'd wake up, sit up in my bed, and he'd be sitting there on the edge of my bed, staring at me, with the bullet hole still in his chin, about the size of a nickel.

I'd start talking to him. I'd say, "Hey, how are you doing?" and his blank face would just show no expression. And after a while, I'd start getting desperate and pleading with him. I'd start asking him if he knew how sorry I was. I'd ask him if he knew that it was an accident. I'd ask him if he knew how much I missed him. Then finally he would open his mouth and try to respond, but just like on that day, the bullet stopped him from speaking, and he just gasped for air. I'd break down in tears, and I'd wake up crying in bed.

And this dream repeated itself for years. Henry always there, staring at me, the same, and me just getting older and older and older. Fourteen, 18, 21, 25, 30, and starting to grey. It took me passing out on the L that day to realise it, but I knew that I needed help.

Now, Henry is dead, and I killed him. No one can absolve you of your sins if you don't believe it in your heart, and I honestly don't believe there's any amount of good I can do in my life that'll absolve me of his death. But my trying to live a life for two people, one of whom I can never bring back, was just a recipe for disaster that was gonna doom me and everyone who cared about me.

It took this chain of events that started with me passing out in public and ended with me having that first tentative conversation with my mother about that day to realise it. And it was an interesting conversation, if uncomfortable. I found out that my mom, of course, had been dealing with a lot of the same feelings of guilt. But more illuminating, she'd been battling anxiety since the day it happened. I think we found some small amount of comfort in learning that little thing about each other.

My marriage died, but I lived on. My daughter's 13 years old now and healthy. I have an eight-year-old son, and he's healthy as an ox. I hope both of my kids grow up to be wonderful people – the type of people who bring so much joy to everyone around them that their absence would be a tragedy, because that's the type of person Henry was.

He died 24 years ago, and it's still fresh. But I'm no longer miserable. In fact, I am well on my way to becoming one of the happiest people I know, and I think that fact would've made him happy. He also doesn't visit me in my dreams any more, and I can finally admit that I'm comfortable with never seeing his face ever again, in my dreams or otherwise. Because at the end of the day, what will an old man like me have to say to his 14-year-old friend that hasn't been said already?

• Listen to Kemp Powers read his story, The Past Wasn't Done With Me

This is an edited extract from The Moth: This Is A True Story, edited by Catherine Burns, published by Serpent's Tail at £12.99. To order a copy for £10.39 with free UK p&p, go to theguardian.com/bookshop or call 0330 333 6846.

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