You cannot transfer a listing from one host to another. Airbnb is host-based, not location based. That means, while you've added him as a co-host, he is not in charge of the listing, you are. The listing is tied to you, as the host, as are the reviews that are associated - because the reviews are about you as the host of that location. You should immediately snooze the listing and make him create a new listing in his own name to take any future bookings.
Additionally, the guests that are currently booked are under no obligation to stay with him as their host. You must inform them so they can choose to move to another property in case they do not want to stay with him alone. Previously they choose the location because you, @Roxane12 were the host. You cannot make this choice for your guests. Finally, you most definitely don't want any changes in the standard of care being shown your current guests to reflect on you and show up on your profile (which they will). He can start his own listing, start handling it in the way he'd like and you can part with a clean break and the reviews for you as the host intact.