I too have a Plex media server at home and while its convenient it only uses my switch bandwidth, not my internet bandwidth.
But if I were to stream videos out to the internet, it will use my internet upload speed which will chew up my monthly cap pretty quickly, since all my movies are in either 720p or 1080p resolution.
So to answer your question, you can share it with your friend, however, you need to be careful not to get caught because what you're about to do is not legal.
On the other hand, you could setup an OpenVPN server and have all your stream encrypted.
But if I were to stream videos out to the internet, it will use my internet upload speed which will chew up my monthly cap pretty quickly, since all my movies are in either 720p or 1080p resolution.
So to answer your question, you can share it with your friend, however, you need to be careful not to get caught because what you're about to do is not legal.
On the other hand, you could setup an OpenVPN server and have all your stream encrypted.