Google has shared libraries where it will automatically share all photos with someone: https://support.google.com/photos/answer/7378858
How can I stop a particular photo from being shared?
When you open the "Shared with name" part of the app, you're then in a folder where you can see everything that is shared with the person. Select the item you want to unshare, then hit the options button and you can remove it. It prompts you and says "items removed from shared library remain part of your own photos library"
This is from the mobile app. I'm sure it's similar for the webapp.