Hi @Melanie189
He already ask you a refund as if it's the most common thing in the world?? From a conditions-only point of view, he has no right to a refund, right? Are You afraid of a negative review?
Try to let him understand the situation from your point of view. That you have a financial loss because you have no chance to get another guest for those days. Would he behave different being a host like you? I don't think so.
Travel companies, airlines, none of them has pity with guests not being able to take the trip. Or they ask for extra fees to be more flexible. Why should we behave different?