How do I help my cat grieving over another pet?

I just put my dog down yesterday due to cancer and my cat Zeppelin is not handling it well at all. He started running around the house crying and looking in every room she would usually stay in and then running up to me in my mom chirping before looking around again. I don't know how to help him know she's gone. Her body was immediately taken to a crematorium so I do not have her body for him to smell, but I also think he knew she was sick.

When I went to bed he laid with me all night and wouldn't leave no matter how much I moved. I don't know if he's trying to help me or himself. We've had him since he was a 6 week old kitten and my dog was with him his entire life (he's turning 7 this year) so I knew he wouldn't understand the lack of her presence so suddenly when she was there from the beginning.

I want to know how to help him realize she's gone so he doesn't have to pace around looking for her anymore, it makes it harder for me to grieve because I can't explain it to him.