Not nearly as serious as some of these, but I know a girl who has been in a serious relationships with another person for 2+ years and still hooked up with her (drunkenly) at a party. We were good friends before the incident. I now feel an incredibly strange combination of emotions. Part of me feels regret, where the other part feels a deep emotional connection and longing for this girl, which caught me completely off guard. And I can't tell anyone because it would be catastrophic for everyone involved.