@Sabrina305 First things first - if a guest threatens a review, and you have it recorded via Airbnb message, you can get it removed. Secondly - if the guest is so hard to please and even has the audacity to still want a full refund and yet continues to stay and while threatening a bad review mind you, you have a 'hustler' on your hands.
Best to accept that, stop placating, talk to him and give him two options: leave (partial refund) or stay and end of whining and threats. Forget about 'I hope he doesn't get more mad', it is all a game with these types of guests.