Help!! My dog cries barks and scratches at the door when I leave

[Casspper]

I have a 3 year old male Shitzu Pom mix I have had him since he was 6 weeks old. He can be really aggressive when I leave (example bite me if I pet him before I head out. Growl at me showing teeth) as soon as I walk out the door he is at the door crying and barking and scratching at the door. I've had several complaints that he does this the entire time I'm gone (sometimes for 8-9 hours while working) he can be the sweetest dogs he had his mood sometimes. I got a cat thinking he didn't want to be alone to keep him company him and the car get along perfectly but he still scratches and cries whenever I leave. I've been thinking about trying some calming treats or something of that nature. Any advice would really help please I'm desperate