Don't be afraid to walk away. Their disrespect of you and disregard for what is important to you is something you should not tolerate for a second, no matter how good the kinky sex is. I'm sure the sex isn't good enough to lose your child over! Your son comes first. There are plenty of other fish in the sea, and the poly sea, who will respect you and act honorably. Close this door and new ones will open.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein