I saw this on an episode of a UK show on Foxtel (am I allowed to say the name?). Here is what was suggested.

If DH is just going to another room for a little while, get Yasin to hold onto DH's mobile for example. "Yasin, you can hold onto Daddy's mobile and while I just go to the toilet". Pick something that Yasin knows DH would never leave without.

If DH is leaving for a longer period and not just to another room, they suggested preparing the baby ie "Yasin, Daddy is going in one hour, how about we play a special game."

He is probably too young but maybe a calender or clock might help. Like DH showing Yasin what time he will be home and making a game out of it.

Not sure what else to suggest but perhaps they might work.