Is my iPhone being hacked by my fiancé

Hacked? No. They may be able to access your phone and it does not involve hacking at all.

• Do they know your Password/Passcode?
• Do you share your location?

You can check what information you are sharing with another person by running Safety Check:

How Safety Check on iPhone works to keep you safe - Apple Support

On your phone......

Tap Settings

Tap [Your Name] at the top of the screen

Scroll down to locate the list of devices using your Apple ID

If you see a device that you do not recognize, whoever owns that device has access to your data on iCloud

Tap on the name of device that you do not recognize

Scroll down and tap on Remove from Account to get rid of the device

Change your Apple ID Password, so they can't access your account and do the same thing again

Hello~ What would make you think that? Do they have access to your device and passcode/password? In the meantime click on below…

If you think your Apple ID has been compromised - Apple Support

~Katana-San~