On your friend's phone, go to settings, privacy, location services, find my and check what is checked under 'allow location access'. It should be the third option 'while using the app'. Go back one level, go to 'Share My Location' at the top of the menu and check that you are listed under 'Friends' and 'Share my location' is switched on. To be sure, switch off his phone and switch it back on. After that, if it doesn't work as advertised, contact Apple and ask them what to do.
All of the above is based on the two of you using an iPhone, if it is a different brand, you'll need another helpful person.