I stay really proactive about these sorts of things our son says. I speak or text with my STBXH right away about things S says that might sound like they came from me, and he has said a couple of doozies! Our son "extrapolates" and also reads a lot so sometimes he comes up with stuff that sounds like it came from an adult.
And I'm careful not to assume that anything crazy S tells me about STBXH, etc. is true. In fact one time I called STBXH to ask if something S said about future plans was true (it wasn't, he left out the "maybe"), and I mentioned that it sure was easy for S to make something sound official that wasn't. This seems to have worked for us but my sitch is less complicated than yours, no living with OW, let alone a pregnant one, and we're both pretty reasonable thus far.
Good luck, and I'm so sorry your son feels that way, it must have been so hard to hear.
I've followed your thread for quite a while now and you sound so much better, and stronger. My H is coming around lately (I'm pretending not to notice, have been following the "setting free" philosophy for the past couple months) and I've kept your story in mind about not getting my hopes up and being pretty firm about the conditions under which we reconcile, if we do so.
