To stop sharing across Apple devices, you need to disable specific features like iMessage Text Forwarding, iCloud Syncing (for Mail, Photos, Safari), Screen Time, Find My, and Bring Devices Together in AirDrop, usually found in Settings under Messages, iCloud, Screen Time, and General/AirDrop, by toggling off the relevant options or signing out of iCloud on the specific device to separate data sharing.
Remove a device
To turn sharing on or off
Press and hold or right-click the network you're connected to, and then tap or click Turn sharing on or off. Choose Yes, turn on sharing and connect to devices for home or small office networks, or when you know and trust the people and devices on the network.
The common reason to this usually occurring is mainly because there is one appleID being used and signed into over two or more devices thus having contacts synced to the device.
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Your wife could see your text messages in a few ways. If your iCloud syncs automatically, or you have backups enabled, your messages might display on other devices that she can access. She might have installed monitoring apps on your phone, or simply be using a shared phone.
Remove your associated iPhone or iPad
Go to Settings > Family. Tap [your name], then tap Stop Using Family Sharing.
When two iPhones are linked, they share information between devices. This includes the same Apple account, iCloud and iTunes information and contacts. It's a quick and easy way to transfer information between devices without the typical process of manually backing up an iPhone and transferring the data via a desktop.
Turn airplane mode on
It doesn't always disable GPS, as these types of radio signals do not interfere with other mobile devices—so you might have to switch this off separately. Turn on airplane mode in Android cell phones and iPhones by swiping the quick access menu and tapping the Airplane Mode button. Fig 4.
View and remove your devices that are associated with your Apple Account for purchases
Tracking apps, including parental control apps, are among the most common methods people use to spy on their spouses. These apps can log your activities, track your GPS location, and even pry into your personal conversations, recording both messaging apps and phone calls.
It can get confusing, because sharing an Apple ID with another family member allows them to see your text messages. This is because iMessage is designed to work across all of your Apple devices, like your iPhone, Mac and iPad.
On your iPhone or iPad, go to the Settings app > Apps > Messages > Shared with You, then turn off Automatic Sharing or turn off Shared with You for a specific app.
How to separate our Apple IDs and share things explicitly?