My wife and I are preparing to separate, and she somehow knows about private text conversations I've had with my best friend about how difficult things have been. I'm almost certain she doesn't know my iPhone passcode or Apple Account password, and I don't leave my phone unattended. Could an old device, synced account, forwarding setting, or spyware be giving her access to my messages? What should I check and secure before starting the divorce process?
4 Answers
Start by checking which devices are signed in to your Apple Account under Settings > your name. Remove anything you don’t recognize, including old phones, tablets, or computers, since Messages may sync across them. Also sign out of all web browser sessions through your account settings. Then change both your Apple Account password and iPhone passcode, and make sure two-factor authentication is enabled.
If you use Face ID or Touch ID, reset the biometric data and set it up again. Make sure the option requiring attention is enabled, because otherwise someone could potentially unlock the phone while you’re asleep. Also review what can be accessed from the lock screen, then change the passcode.
There may not be spyware involved. Someone could be seeing messages through a shared Apple device, a forwarded message setting, a synced computer, or even information coming from the person you’re texting. It’s also worth changing passwords everywhere and replacing any default voicemail PIN, since voicemail access can reveal private information.
Review your Messages settings, especially Text Message Forwarding, and turn it off unless you knowingly use it. Look through your installed apps for anything unfamiliar, and check Bluetooth devices for a shared computer, car, or other device you don’t recognize. If there’s any doubt, remove the device or app and change your credentials.

I checked the connected devices and only found my phone, work computer, and an Amazon Fire TV device. I appreciate the suggestion.