This exact same thing happened to me. In elementary and high school I found making friends very easy. I had friends in every class, in every clique/social group, I was well-liked. But I put all of my eggs in one basket -- my best friend from childhood, who was lovely as a kid but vicious, judgemental and cruel as a young adult -- and it led me to kind of downplay my other friendships. Eventually she decided she hated me, like she'd done to numerous girls in the years prior, and it was so painful. We'd been best friends for twelve years and it felt like having my heart ripped in half. She told people a bunch of weird lies about me, to get them to not like me. She told them I was elitist, but I'd grown up poor. She told every guy friend we knew I wanted to have sex with them, which led to a LOT of awkward conversations. And weirdest of all she told them I was supposedly "racist" even though I literally worked for an Indigenous artist and applied to study Islamic feminism at university, so it was evident I didn't have a problem with diversity. Even though our mutual friends told me they knew she was bullshitting, the whole experience was way too painful. I knew if I kept contact with them, she would never stop hunting me down and trying to hurt me. Because that was what she'd done to other girls. So I just cut off contact from everyone and spent my entire gap year alone, working, with virtually no socialization outside of a coffee or two with my elderly coworker.

It honestly fucked me up and scarred me and made me terrified of socializing and bonding. I'm so awkward now, so socially unaware. I'm so scared that people will hurt me again if I let them in, so I don't make friends with anyone. I had no idea people could be so cruel.