I'm not going to let my ex spend time with our autistic kid in my apartment
Why not? They are the parent, too.
I will just feel uncomfortable and I don't think it's a good experience to have with the kid.
I think that you should let them see the kid. They are the parent too.
He's not a good father. He don't deserve to see them.
If they are a bad parent, then go to court and prove your case to a judge. Otherwise, allow the child's other parent to see them.