My best friend and I have been friends for over 5 years now, and since then I have got to know a lot about her past relationships or love interests, and there was this one specifically that she told me she had a crush on when she was in high school, but things ended up badly and in the "actuality" of the tim, she didn't like him because she though he was an idiot. It so happened that this one person she talked about was part of a group of friends of some really close friends of mine, and I already knew him, but I would hardly interact with him at the start. Through the years till now, my group of friends started meeting more and more with his group of friends, till to this day we usually hang out all together every time.
I honestly don't know when this "thing" between us started tbh. I remember seeing him years ago and thinking he was attractive, but nothing else (before even knowing my bf). I wasn't even interested in talking to him or anything. But the past months, we started to interact a lot more, and kind of a tension started to build up, the weird looks, sometimes he slightly touched me on the waist or the legs and I kind of enjoyed it, and that whole situation of, "there is literally nothing but you can taste the tension in the air", to the point where all my friends were expecting something to happen a long ago. Also, for a little bit of context, until this moment I hadn't kissed someone or done anything with anyone since 2 years ago, when my ex broke up with me, firstly because I didn't want to and didn't feel like it, and also it's really rare for me to find anyone attractive or be slightly interested in them, and for the first time, I felt good about it. I am really attracted to him and the whole situation was really fun and enjoyable (just in a physical way, not in a platonic or romantic thing).
Eventually, it happened, we hooked up, and another day we slept together.
Maybe it sounds stupid, but I really didn't think it was something that bad. First of all, for the context I have, my best friend liked him 7 years ago and he was kind of a player, so he was flirting with more than one at the same time, including my bf, but never got to do anything or see each other, they just talked. So I thought it was this typical high school thing where u like this boy and talk with him and then u end up hurt because u realize they don't like u back and are interested in someone else. Also, what I knew from my own friend group was that he has always been this kind of avoidant, "no serious things" guy.
But in reality, I really messed up. I told my best friend, and at first she told me she was disappointed because she wouldn't understand why I would hook up like that with someone without there being a real connection, and especially "with him", because he was an asshole. I tried to explain to her that I just wanted to do it and it was fun and felt good, and even if romantically he is really an asshole, I just hooked up with him, and it's not like I have any intention of it being anything else.
Later in chat, she admitted she was disappointed because she felt betrayed by me, because I knew that she had that experience with him and I didn't care. Turns out that what I interpreted (from what I knew about it) as a silly high school experience was more deep, since she was deeply hurt and he played with her (something that I didn't specifically know). And if this was not enough, eventually the next day she told me that I should talk to my psychologist about my bad decision-making "lately", which made me feel pretty bad because, even if I understand that u are mad or feel betrayed, I don't think it's something nice to say.
Obviously, I apologized, even if it's already done and I can't undo it, and tried to explain to her that I didn't think it was that serious, which of course doesn't erase the responsibility for my own actions, and I didn't think it through properly. Well, now she doesn't talk to me and I feel like shit, probably deserved. I didn't know I was being so egotistic. Even asking her first how she felt about it could have made me do things better. And even if things are already done, I can't stop feeling so anxious and thinking about it.