What you want is a dedicated server. (check guides section or youtube)

Run it on your PC, or the friends PC, or buy one for pretty cheap from hundreds of server providers.

For first two options you'd need an external IP address with ports open, not every internet provider offers this nowadays, some can be convinced to allow it if you talk to them thou.


If you cant assure any of the PCs running when the other person wants to play, and dont want to spend more money, then technically you could synchronize the save files over the internet, but that question is more for the google.