A friend of my boyfriend, who is a girl, confessed her love for him in a letter that she put under his door. My boyfriend refuses to let me see the letter and says he loves me. He continues to still text the girl and just recently saw her when going to visit his friends. He ended up sleeping over her house alone with her but, swears nothing happened. I don't trust either of them at this point and part of me wants to make both of their lives a living hell.