Once when I was in high school, I was sitting down with two friends when three beautiful girls approached us. I didn’t know any of them, but my friends did. Two of the girls were evidently friendly enough with my pals to sit on there laps. For a brief second I really felt sad that my lap was empty, but the 3rd gal took notice, and asked to sit on me. I will never forget her for that. I wish I could tell her how amazing that made me feel. My friends were more popular than I was… I was a quiet kid. I still think about her to this day, and hope she’s well. I really want to tell her that it meant so much to me to be included.
For almost 30 years, I called you my best friend…in the last 15, I chalked it up to the drugs that addled you and made you behave in selfish and shitty ways, but I recently looked back at our lives and it wasn’t the drugs… you were just kind of shitty. I wasn’t always great either but I never had the malice that you’d show. My confession is that… I don’t wish you well. I just hope your ex and your kids do well.
You really were my favorite dog, Trixie. 
I should’ve listened to you Daddy, the one time I didn’t was a massive mistake. I’m sorry.
Mom,
I’ve been having dreams about reconciling with you. They aren’t happy dreams. In the last one, it caused me to lose my job and alienate all my coworkers.
I know what this means.
I don’t love you. I thought I did, but I learned I can’t love you and myself at the same time, because you are the antithesis of me. But I no longer want to define myself as just the opposite of you. I’m so much more than what you aren’t.
I’m sorry for you but that’s all it is, pity. I used to worry about what’s going to happen to you when you’re old, but honestly? You have twenty years to figure it out. Good luck.
I’m really happy others have contributed.
Hey, high school girlfriend: I want to apologize for being boring.
Most Friday nights started with us (and usually some friends) hanging around your kitchen with the newspaper spread out on the table, looking at the movie times. At some point someone would shrug and say “Well, we could always see Butch and Sundance… again…”
We saw that movie seven times that summer.
Come on, WHY didn’t I take you to a concert, a play, or the symphony, or find a new restaurant? (Because we were all just dumb kids, I guess…)
.
Well, anyhow, since you’re married to my best friend, I could tell you all this in person, but it seems like it’d be awkward…
To almost all of my male partners, I was faking it every time.
Nice! Any luck with the gals?
I’m a dude, but I’ve faked my share of orgasms.
Hehe. I SO get that. That movie was pure magic. I desperately wanted to be Katherine Ross riding on the handlebars of that bicycle. “Raindrops keep fallin’ on my head…” 
As for the OP, I will think about this and post later. I missed this thread the first time around. It’s a great idea.
I never apologized to Stanley. I punched him in the face in 3rd grade. Broke his stupid nerd glasses and bloodied him up.
Ok…ummm…still ain’t gonna. You little creep.
Wow. Thank you. 
To best friend from middle school to beyond high school: I know you were seeing my first boyfriend behind my back. I saw his phone bill on his coffee table, and he had racked up hours talking to you - I recognized your phone number. Other little clues and hints also pointed decidedly in that direction. I didn’t confront you immediately, because I was too young and naive, but when I matured a bit and was seeing my next boyfriend, I ghosted you. You tried to contact me a few times, both back then and later when the internet came about, but I didn’t respond.
Well, you died in 2007, and did so without knowing why I ghosted you.
This is very embarrassing.
Les, I’m so very sorry for the stupid, ignorant and awful reason I gave you for not wanting to date you. I should have just said no. Or better yet, said yes. I really liked you as a friend so maybe we’d have actually been great together.
Marta, I’m sorry, but you deserved the punch in the nose. Regardless, I hope you’ve found happiness.
I like this thread.
I was a draftee, and I regret not telling one of my C.O.s that I would soon be out, and he’d be nothing but a bad memory.