Facebook provides numerous privacy options that enable you to determine who can view your posts, pictures and other information. Along with general settings, you can change the privacy settings for a single status update, as well.
The audience selector tool on the status box allows you to share your post with the public, your friends or a custom audience. If you select “Custom,” you can choose precisely who sees the post — from one friend to an entire group.
How to Let Only One Person See Your Post on Facebook
Here are the few steps you can follow to let only one person see your post on Facebook;
a. Click inside the “Update Status” box and type a post or add a photo or video.
b. Click the “Audience Selector Tool” button next to the “Post” button and choose “Custom” from the drop-down list.
c. Click the “These People or Lists” drop-down in the Share This With section and select “Specific People or Lists.”
d. Begin typing the name of the friend with whom you want to share the post. Select your friend’s full name when it appears. Click the “Save Changes” button.
e. Click “Post.” The post is only visible to you and the friend whose name you selected.