That moment you know you picked a good one

So I am probably going to come off as extremely laid back, maybe too laid back. I don't want to go into a ton of details, but my SO and I are visiting someone's house. One of the people here is his sisters friend. 
Since we've walked in the door this girl has been watching my boyfriend. You don't have to be paying attention to notice it. I legit caught her looking at us from behind a door and when I went to make eye contact she ducked like lol you creepin. My SO hasn't even aknowleged her. So I've been upstairs watching TV, it's like 3 am and my SO has been down stairs with everyone. They let me do some laundry so I walked down to switch it and I see her standing Infront of him. Like she had just stood up. Everyone else is passed out, she goes to put her hand on him and he SLAPS IT AWAY and gives her this gnarly ass look like "the fuck you think you're doing ya nasty" and he just walks around her while keeping this ugly look and staring her right I in the eye. and walks away. I am trying not to laugh, I'm like almost choking and my head is about to pop and I see him start walking so I like probably so obviously went back up the stairs and laughed like an idiot. He walks in and looks at me and shakes his head and just still has this "the fuck" look on his face. He hasn't even said anything 😂takes off his jeans and puts on his pajama pants and passed out next to me. I picked a winner you guys, and im still trying not to laugh. I ca t decide whether or not I want to bust out laughing or go down stairs and clock her in the head. But I've controlled myself this far I think I can manage😂