@Lucinda28 Have you written a review for him yet? If not, his review won't be posted until 14 days after the stay ended.
How do you know he wrote a review for you? Did you get the notification and actually see it, but it's not showing up on your listing yet? Maybe he just hasn't written one.
Is he from out of the country? If so, his review will appear at the bottom of your reviews, rather than as the most recent.
Finally, if none of these things apply, sometimes there's a glitch in the system where reviews just don't show up. If this is the case, contact Airbnb and tell them about it, and they will fix it. It was happening to me for a while, but it eventually stopped happening.