My (22F) boyfriend (24M) invited his girl friend back behind my back, how do I confront him?

My boyfriend is going back to school next year for engineering. He is moving out of my house this weekend and invited me over to his place to finish packing. <br><br>Well my guy friends from high school that I still keep in touch with, invited him to their house to hang out and drink. I picked him up from my house and we got to their house. There, I was introduced to another girl, let’s call her Jess. <br><br>Jess is a mutual friend, but I didn’t know her well. She is hot and definitely not his type. I could tell by the look in his eye when he met her, and how he was talking to her all night. I could tell that he was into her, but I thought that it was fine because she already had a boyfriend. <br><br>The night went by and I could tell he wanted to leave, but she suggested we all play a game of spin the bottle. Spin the bottle is a game where you spin a bottle and kiss the person the bottle lands on. This game usually involves people you already know, and it’s not a kiss on the lips. However, this time, the bottle landed on each other twice, and each time, they kissed. <br><br>I got in my car and called my best friend to check if this situation was weird. My best friend agreed that it was weird, and she told me to just go home and confront him about it. So I did. I gave him the benefit of the doubt, and asked why he didn’t tell me that he was going to play kissy kissy. He said it wasn’t a big deal, and that she was single. <br><br>I checked up on him tonight to see how his move went, and heard from one of my guy friends that he’s been texting Jess all day and night. How the fuck am I supposed to confront him about this? I want to leave him so bad. I want to scream at him, but I don’t want to do anything that would make him defensive, and have him not want to change.<br><br>TLDR: my boyfriend invited another girl back behind my back to his empty house, how do I confront him?