I was terrified by her reaction, knowing that it was an absolutely horrible thing to do. On the following Monday, she brushed it off. She said, “I ended things.” I took this as permission and fell head over heels. It was the kind a first love where you talk about baby names and then scream at each other for a imagined indiscretion. He was all I thought about and talked about. This created tension between Sadie and me. At first, she rolled her eyelids and pretended to not care. Her ego was clearly bruised by the development. But soon, her behaviour changed and she became more reserved at school. She would get drunk and then throw herself on Tom to see if she could “steal him back”. She then started doing the same thing with other friends’ boyfriends. She was apparently determined to prove to herself that she could also steal someone from someone else. All these attempts at karmic vengeance only led to her being slowly pushed out of the group. She and I never talked about what happened. Both at the time and years later, I would justify myself by believing that I was in a relationship. As a romantic at heart, this made it all okay. My relationship with Tom was marked by certain milestones. First, it was how long we had been dating. Then, it was about the big firsts, like having sex, getting to know the parents, and going on vacation together. If we were going to the end, I thought it didn’t matter that he had dated my friend before. The rest of my friends didn’t seem to care, and largely followed the same logic as I did. Tom and Sadie had a brief, insignificant encounter. It was a life-changing, transformative, and earth-shattering experience between us. Until it wasn’t. We broke up three and a quarter years ago, and I haven’t spoken to or seen him since. I will never be able to tell if dating the ex of my best friend was worth losing her. I look back at that time and feel great sympathy for Sadie. She did nothing wrong but poorly communicate her feelings about the situation, and then acted out of hurt. I was a teenager too, but does that make me any less guilty?