Not all friendships are built on a good-faith foundation. You could be in a friendship with somebody for years just to realize that they have resented you virtually the whole time. Typically, it's easier to avoid making friends who hate you when you're an adult versus when you're in high school. I had so many friendships just fall apart from the time I was 13-18 because my friends just started being insanely cruel out of nowhere. These days, I do not have time for anybody who treats me like garbage, which makes things a lot easier.
Some Twitter users recently shared their stories of besties gone wrong, and some of them are so dark-sided sided they make me feel so much better about my bad friendships. My best friend started totally ignoring me in group settings during my Sophomore year, but at least she didn't steal my husband and lie to me about it!