I unintentionally fell for my fiances sister. She’s been staying at our house for almost a year now. Shes 19 and I’m 28. Nobody ever thought we would become this close but when you drink and smoke and talk for hours week after week with somebody, it’s hard not to bond. One night my fiance went to work and we hung out until 1 am. We had this game where we would challenge each other to get the most fucked up we could possibly get. Well she starts throwing back shots and drinking beer and quickly becomes white girl trashed in under an hour. I wasn’t on that level yet and I didn’t want to cruise and walk around with her falling and stumbling everywhere. I offered my arm for support and she fully embraced it for basically like the next 4 hours that we drove around and while causing mischief around the countryside. I couldn’t help by get hard fantasizing about all the stuff I had only had thoughts about up until this point. I couldn’t tell whether she felt the same but this was really leading me on. So we get home later that night and she can barely get out of my truck. I can’t tell if it was an act or not but thats what she made it seem like. I walked around to open her door and she threw herself on me. I was still hard at this point and there was zero chance she didn’t feel that. I laid her on the couch and started to give her water so she didn’t feel bad in the morning. I went and showered quickly and came back to find her still on the couch. She again said she was incapable of moving and wanted me to carry her. I did. I got her all tucked in and really had no intention of staying unless i got the sense she wanted me there. It didn’t take much to convince me when she pulled me close to hold each other and talk. I kept explaining how we couldnt be doing this and it didn’t matter how much I wanted it, I needed to leave. We sat there for 10 mins or so just savoring the moment when I instinctively kissed her neck. It’s just something I do to her sister all the time and I didn’t even realize I was doing it. But a second later I felt her innocent kiss on my cheek and she aligned my face so that we were about to kiss on the lips. I just smiled and backed away. I said if only I had known you in my younger years, we need to stop. She said why not? I said you know why. And I left. I probably would have done it had my fiance not been in the room right next door. She was a virgin up until this past week when she met some ronchy dude at her workplace. I’ll probably regret this my entire life. But hell, if I had done it, the shame I’d feel looking into my fiances eyes would probably also make me want to off myself.