My boyfriend has a stepdaughter & his girlfriend is having a threesome with him. I think that he saw my blog post about his stepdaughter because he is so familiar with it, but what he didn't see was the fact that her girlfriends also had threesome with him. My boyfriend is taking me for it because he thinks that I am dating his stepdaughter too. He confronted me and I told him that it was completely wrong, but he thinks that it's fine because he sees his stepdaughter as a mature woman, which I guess is true. How do I tell him that I think my boyfriend is having a threesome with his stepdaughter & his girlfriend?.