I found an old chat between my girlfriend and a guy.
This happened a few months ago, but I remembered it today.
She has a tablet where she set up her Instagram account. One day she went to university and left her tablet at my house (I admit I went through her chats and stuff, which isn't exactly right). I found a chat from about a year ago with a guy where they were talking about getting together to have sex. He was asking her questions like, "Have you ever been tied up while being fucked?", "Are you going to suck me off?", "Can I slap you and cum on your face?", to which my girlfriend responded with messages like, "Yes, please cum on my face, I've never had it filled with sperm." "I'd like to be tied up while you fuck me doggy-style." "I'm going to suck you off on my knees while I look into your eyes." "If you want, you can grab my hair and use me however you want." A couple of messages later they were talking about coordinating a time for the meeting that same day, and then a message from my girlfriend saying, "I'm here, I'm outside your house." Then several hours passed until nightfall, and finally a message from my girlfriend saying, "Thank you so much, I had a great time today <3." What really turns me on and makes me incredibly hard is thinking about those hours without messages right after my girlfriend's message saying I'd arrived, probably because she was being choking by his cock, completely submissive, on her knees, looking him in the eyes while he grabbed her hair and her pussy dripping wet. Thinking about how the other guy must have made her his bitch, and then her sweetly saying goodbye with a "<3."
She doesn't know I saw this and I haven't told her about it.