Orange, your son is 3, he's not a reliable source of info. You can't use his words against your W in a court of law. Talk to your L about whether S3 sleeping in OM's bed is info that would help in court, if it is then ask your L if you should hire a PI to gather evidence that it is taking place. You're wasting your time trying to get W to admit it and just building animosity between the two of you. Here is what I think, I think your L will tell you that it doesn't amount to a hill of beans in court because you're already separated. And if it doesn't, then you just need to let it go. I completely understand that you don't like it and why, but the long and short of it is you two are practically divorced (you are already calling her your ex) and as such, what she does with S3 when she has custody is completely out of your control (unless he's being harmed in some way).
Also your entire conversation with her was the very definition of passive/ aggressive. This is something we've mentioned before that you really need to work on, and it sure doesn't seem like you've made strides on that. I can't remember if you're seeing an IC but if not I would highly encourage you to do so and bring up this particular subject with them.
