I've come to realize that I'm afraid of SS10.  Maybe afraid isn't the right word, but I feel very unsafe around him, and I'm trying to identify if it's rational or irrational fear that's driving it.

He's 10 and I've known him his whole life. He has significant speech delays--mostly expressive, but some receptive--as well as a host of other developmental issues, according to his most recent psych assessment.  He has never had a friend and doesn't understand social norms, though he can read emotions and is quite introspective.  He lacks empathy almost entirely, except for his HCBM, who he wants desperately to please.  Not on the autism spectrum, per the psych.  She also called his behavior anxiety-driven instead of conduct disorder.  Has been in "therapy" for years, but there are no defined goals and no discernable progress.  His therapist is useless.

HCBM hates me and DH.  She engaged in moderate PA several years ago--to the point that SS refused to see DH for almost a year.  SS reports that she told him to be mean to me, but I don't know how reliable that is.  Goodness knows he's not nice to me.  I don't think he ever even calls me by name.  He has the psychopathic stare down pat.  

He slinks sliently around my house when he's there.  He eavesdrops.  He lies twithout compunction.  His behavior is never out of control in our house, as he knows DH wouldn't have it, but at his HCBM's, he's king of the roost.  He does whatever he wants without consequence, but it's usually not violence, per se, though he did throw a knife at his sister not too long ago.  His mother has him in martial arts and he plays violent video games.  His teacher is quite concerned about what she sees in the classroom (identifies him as lying to get his way, holding a grudge, deliberately annoying people, etc.), though he claims to be bullied regularly.  Earlier this school year, he threatened another student that he was going to "murder" him and lied to the principal with no real conseuquence at home or at school.  DH feels powerless.  HCBM has primary custody, so he's a prison warden when SS is in the house, but she won't do anything when SS is with her, which is most of the time.  And the punishments at our house never seem to accomplish anything.

I'm literally afraid that I will wake up to him staring at me in my bed or that he will slit my throat or something.  Don't get me wrong, he's tiny.  Well less than 100 lbs., lacks processing speed and is weak, even for his size.  Looking at him, the fears seem completely irrational, but I can't get over my gut instinct that there is something wrong here.  

DH and I have developed a safety plan for me/DD.  We are never alone with him.  He's not allowed to care for my dogs (he proviked a dog to bit him a couple years ago at BM's, and no one really knows how).  We have cameras throughout the house.  I don't discipline or assign tasks.  

I'd like to figure out whether I should work on getting over the fears, or if I should listen to my gut.  I spoke with DH about it, and he feels they're irrational, but it's his kid, so I'm not sure he's reliable.  Ther psych was just enamored of him (in fairness, he's tow headed with the longest eye lashes you've ever seen), and as I mentioned, his therapist is terrible, so there's not really a resource for me to go to on it.

What say you all?