>IP address?
>
>Is this like a social security number? Is this assigned to me for life?
No, IP addresses are usually temporary, refreshing every few days or when you reboot your modem/router.
>If I have an iPhone and say, I get a new iPhone does my address change?
The device will have its own MAC address (permanent for that device)
>If I move my home and get a new Internet provider does my address change. ?
Typically yes
>The reason I’m asking for content.
>
>Let’s say my ex wife was spying on my phone. And was somehow receiving an email that had my internet activity on it.
More likely being done via something on the phone or via your Apple account - did you have you ex's phone on the same account or any old devices still connected to your Apple account?
>How could I stop that moving forward?
Check for dodgy app's on your phone, make sure old devices are removed from your Apple account