How can I prevent a user that I have shared a Space with from seeing it after I have shared it with them?
You can always remove that specific user from the Space as long as the Space shared is “private.”
If you chose “public” when you shared the Space, you can go back into your permissions and edit to “private” and then remove the user. Or you can add an access code for the Space. Only the users with the access code can access the content.