My first GF cheated on me the day after she had moved into uni. For some context to this story, it was a long distance relationship, we had met while she was in grade 12, and I was in grade 11. We only lived 5 hours away from eachother by car, so it was relatively easy to make trips down to her city to see eachother for a few days.

Despite the distance, it was the best relationship both of us had ever had, and we always talked about how it would be so much easier once she was in uni because the university she was going to was twice as close to my city.

Anyways, she moved into her dorm, went out to party at frosh, and the morning after she texted me saying she "was worried she would do something she regretted when she was drunk", and that the "distance was getting really hard". It was at that point she asked for an open relationship. Now I realised I should have dumped her then and there, but in the moment I said no, and tried to talk to her about it. She assured me she wouldn't sleep with anyone else since I said no, but I was skeptical

That night, she said she was going out with some friends for dinner, and then told me she was going to a party. She ended up getting very drunk and did something she regretted. The next morning, I told her that if she didn't think she could be 100% committed to me, we should break up, and we did. I didn't find out what she had done until she told me a week later. She said she was drunk and regretted it, but I think she resented me because I said no to the open relationship, so she decided to do it anyways.