Death of a family pet.

We had to have our cat pts a couple of months ago. Our son is 10 and is autistic. He was upset at the time but seemed to deal with it ok. However the last few days have been extremely difficult. His grief is overpowering and I'm at a loss about what to do. I've tried everything I can think of to help him. He is sleeping (if you can call it that) in our room because he thinks I will die if he's not with me. He also talks a lot about dying and about him dying. He's scared to sleep, he doesn't like dreaming because he can't control them. We are waiting for an app with the paediatrician but if anyone has any ideas in the meantime I would be really grateful.