1. Be the 'social media' freakIf you are added to all his social media accounts then bombard him with love messages, start liking every post of his, make it but obvious that it's he who you surf around even on the internet.
You can also start by making a collage of your photos with him, post it and start tagging him and some of your mutual friends.
They might get shocked with such intrudance into their social life and may ask you politely instead to walk out... and Bam! It's done!