How accurate is my boyfriends location when tracking him in find my iphone

Howdy! There are multiple factors that go into the accuracy of "Find my", and they all depend on how the feature works.

Basically, "Find My" uses a combination of GPS, cellular towers, Wi-Fi, and Bluetooth. So the accuracy of "Find My" would vary depending on the reliability of these features in the situation. For example: perhaps you've lost your iPhone in a crowded mall. In that case, it might be very accurate, as other iPhones contributing to the "Find My" network would be using Bluetooth, the iPhone may be connected to the mall's Wi-Fi, and GPS and cellular is likely to be good. However when lost in a rural environment, "Find My" may be working from GPS alone, which would be considerably less accurate.

To answer your question in a more short way, it just depends. For more information, see the links below.

https://www.iphonelife.com/content/how-accurate-find-my-iphone-tips-to-improve-accuracy

Locate a device in Find My on iPhone - Apple Support

iCloud - Find My - Apple

Use the Find My app to locate a missing device or item - Apple Support

Hope this helps!