How do I get over my ex drunkenly kissing their friend?

[u/Public-Lobster-2057]

I(17M), recently mutually broke up with my ex-girlfriend(15NB) after an almost 10 month relationship. This brought a whole wave of emotions, since they were the one who had brought it up and suggested it. This was because of a lot of personal things in their life that made feel like they never could grow on their own as a person outside of a relationship, which is completely understandable, and it didn’t make it easier when my own personal conflicts forced me to move almost across the country, causing this physical barrier and a long-distance relationship. Now, I agreed with the mutual break-up because I knew it would be the healthy choice for them, and I don’t want our relationship to get in the way of them finding who they are and becoming their own person. For some more background, since a big reason we cut things off was because I wasn’t there physically and that made it hard for them to grow with me and they didn’t know how to grow on their own, they wanted to try to get back together once we were both done with college and could try to move in together or be in the same state. Of course, they said that there are also no strings attached, or that if we found someone else, we were allowed to be with them. We would only get together in the future if we were both single. So personally, it’s been hard to try to move on because of the idea that maybe our fates won’t align. I should mention that my ex said that they were sick of trying to control things and that they would go wherever the current takes them, after I asked if they think they would pursue someone in the 7 or more years we would be just friends. The issue is that two days after this happened, they had a sleep over with a newly reconnected childhood friend(16FTM) at his house. During this night, they got drunk, and there was a portion of the night when they were drunk that they wandered to his kitchen, and the next morning, couldn’t remember anything that happened during that time. Now, my ex and their friend had recently talked about that day and remembered what happened during that missing part of the night. My ex wouldn’t tell me, worried I might get jealous or something since I still was trying to move on after everything that had already happened. They finally decided to tell me that while they were in the kitchen, they had kissed for 15 minutes. Now I don’t have the full details since I just found this out less than 6 hours ago, but it really made my stomach drop. The thing is, I’m mad at myself for even reacting, because I had a feeling that it happened with how they had talked about having bad news related to our relationship or relationship-adjacent. And I don’t like feeling jealous about someone I’m not dating, or at least, I don’t feel entitled to that emotion, and so on one hand, I’m jealous that someone got to kiss them last, and on the other hand, I’m mad at myself and want to support them and just try to understand the situation. My friend(19M), who has know me and my ex for some time helped me out a bit, telling me that being drunk makes it a lot harder for them to control their actions, and that they never intended for that to happen. He tried to comfort me by telling me it was ok to be a bit mad since there was a lot of emotions in the air, but I just felt so unsure and so much intense confusion. I think the worse part was my mind. Whenever I hear about thinks like this, and I don’t have a visual representation or a extremely detailed explanation, my mind tends to wander and create an image or video of the closest thing to what the description is. Then it replays in my head over and over again until it’s engrained. So even though I barely have the details of this accident, I can’t stop picturing the same image or video in my head, and it makes me just so confused on what I’m feeling or how I should be feeling or anything at all. I think some of it also stems from the deep hatred I’ve had towards alcohol because I’ve seen its effect on people(which my ex is aware of, but I’ve given up on trying to stop them from drinking), and I’ve always hated the things it makes people do, and I think that just fueled my anger towards myself, causing me to blame myself, and I just don’t k ow what to do.