iMessages Permanently Shared Location - Are They Tracking Me?

if you see this arrow icon, that means that your iPhone is accessing your location:

• A hollow arrow means that some apps (one or more than one) are actively using geofencing. This means that this will trigger an action when you go to a set location. For instance, you may set up a location based reminder (e.g., “set a reminder to call Bobby when I am home”) and when you are home, you will be notified. Obviously your iPhone will have to use Location Services.
• A solid (black) arrow means that your device is actively accessing your location. For instance, when you use a Map app, you will see this.

You won't know if others (with whom you have shared your location permanently) are following you.

I suggest that you go to Settings>Privacy.... then scroll down to the bottom and read the meaning of the "location arrows" (when they appear).

If you allowed some apps to use your location, to my knowledge it means that those apps are using your location, not the apps user.

Regards

Giulio