Prepare him for the separation
Before you start to leave your pet alone, start to ignore him partially, which means, show less eye contact or less comforting them. Engage with them in small conversations and certain activities as follows.
“Dear, it’s the time to leave for office now”; “could you go and get the keys for me”; “ok go soon and get the key”; “I am going to miss you now”; “don’t worry dear I’ll be back soon”; are the words that sounds in rhyme yet firm, could prepare him for the separation. It definitely works over a period of time.
Leaving in familiar places
Pets usually goes to a fearful mind state when we leave them alone at home, so always leave them in specific familiar places in the home that is usually confined for them. There they can be comfortable or can manage until your arrival.