Muddle, honey, I am still here, and still wanting to kick your W's a$$, OMGosh. She makes me so mad.
Forget HER in C, I don't give a rat's hind-end about her therapy at this point. is your SON in C? As you have said, that is a LOT on a small guy and he needs someone to talk to that he can be completely honest with about how he feels in his little head.
Unfortunately that cannot be you, either, b/c he feels -to some degree- that he has to be strong for you, or just not his complete wide-open self on this topic b/c it's painful to both of you and I'm sure he wants to spare you pain (as evidenced by his sweet comments in the face of your W's crap).
Not that you can't love the heck out of him and make him feel as secure as you possibly can, of course you will!, but he needs a safe 3rd party to process this with.
Forgive me for butting in on that, but I have a friend going thru a horrible separation and her middle child (very young) has been crying every night "wanting to die" unless daddy moves back home. He actually found a dagger from an overseas trip on a high shelf and put it to his abdomen wanting 'to die unless daddy comes home'. She went that night and got her H and put him in her son's room for the time being. She said she'd rather be miserable for all eternity with this horrible man than to lose her little boy over it. (who is now in C, by the way)
SO. all that to say my red flags are waving in your situation due to what I've seen here locally. not that anything so drastic will happen to your boy, but I'm just saying.
Forget the former things; do not dwell on the past. See, I am doing a new thing! Is 43:18-19
If it seems slow in coming, wait. It's on its way. It will come right on time. Hab 2:3