I had the same best and only friend from kindergarten to fifth grade, and looking back it was basically an abusive relationship, as ridiculous as that sounds when we're talking about children.

He was my very first friend, I had been extremely sheltered from other kids until kindergarten started. He wouldn't let me have other friends and would pick fights with anyone else I got too close to until pretty much everyone just fucking hated us both (him because he was mean and me because talking to me made him be mean to you and I wouldn't say anything because I was terrified I'd lose my only friend), he wouldn't share anything with me the way kids usually do, he'd make sure to let me know how bad I was at things, he lied about random shit nonstop and if I ever called him on it he'd get pissed and start ignoring me (devastating for a child who has no other friends), he stole shit from me and stole other people's shit and let me take the blame for it, he made me run back and forth across the playground sending messages for girls he liked, and at one point in fifth grade even asked me out out of nowhere and then after I said yes he "took it back".

By the end of fifth/beginning of sixth grade (so around 10/11 years old) it finally ended because he wanted to be cool and I was incredibly uncool. He mostly made himself cooler by openly insulting me in the halls while with his new posse. Which is fine, because in sixth grade I made an awesome new group of friends, several of whom I still talk to today at nearly 30. There was one tense final standoff in sixth grade though where he apparently had heard from someone I said something homophobic about him and a teacher forced me to apologize, which is hilarious because he was the one who'd been saying "if I ever had a gay son, I'd kill him".

Looking back, man...that was all kinda fucked up. Why the fuck was he like that at such a young age, and why was I such a huge doormat at such a young age? That was some shit.