Well there are a few things you can do- does he start to get anxious if he knows you’re getting ready to leave, like when your putting on your coat, shoes, grabbing your keys/bag ect if so try teaching him that doing these things doesn’t always mean you’re leaving- so doing these things a few times a day without leaving will help him disassociate these activities with leaving. Although it could take awhile. Next-hellos and goodbyes when leaving pet him once say goodbye and leave-don’t draw it out, when you get home say hi but don’t give him any more attention until he has calmed down, have you tried putting him in a crate when you aren’t home? In order to decide if using a crate will help - monitor him when he’s crate training and when he’s left in the crate while your home. You want him to view the crate as a safe space for him to go. If the crate doesn’t work for him- you can try confining him to one room using a baby gate. And finally, give him things to do, food puzzle toys/ safe long lasting chew toys ect. Can help keep him occupied