Since this is the place where even lawyers go for advice, here goes.
I have the perfect arrangement for my first threesome. A regular favorite (DS III) and a friend of hers that she's in love with. I know and like them both. They are both hot. They like to make love to each other, they're willing to do everything for a reasonable price. They have some experience doing threesomes. It's everything that I've been looking for.
It's perfect. Except. DS III's friend has a boyfriend. He recently beat the crap out of a guy who was messing around with his stripper gf. In his defense, it sounds like they guy was trying to rape his gf. So any of us might have done the same thing. But the cops arrested the boyfriend for assault which suggests that they thought that he beat the guy more than was necessary for her defense. The guy was not a strip club customer, just a guy that his gf knew and considered a friend. So this was not an OTC gone bad.
So the question is should I do it? Is it worth the risk that the boyfriend could possibly pose? The boyfriend knows that she is a stripper, but I don't know if he's aware that she is sometimes a prostitute. DS III knows my identity. The friend does not, unless DS III told her which I doubt. I trust DS III. I don't know the friend very well.
If I did this it would be at a hotel, not my house. But DS III knows where I live.

