Do you worry people might avoid your site/shop due to stigma around loneliness? I am curious is people might end up being embarrassed to be around because they would get designated as "lonely". If you find that people are slow to sign up, you could potentially do some A/B testing and advertise the same idea with a name that is related but feels like it has a more "positive" twist to it?(Could be called "Ludo League" [Ludo being the Latin root for 'game'] or something. Sorry I am crap at coming up with decent names lol)

Also, since you are in Germany, have you considered going to the next Spiel Essen board gaming convention? I haven't gotten the chance to go yet, but I imagine it would be a good way to make a lot of connections and get your gaming group known to a bunch of people.

Also, boardgamegeek/rpggeek are places where you could get your name out there(just in case you don't know about those).

Lastly, not sure how common board gaming shops/communities are over there but they are quite popular and common over here in the US so if there is any extra stuff you need to know regarding gaming shops you could probably get a lot of useful info by googling (random big US city like New York City) + "board gaming shop". Star City Games is a super popular one here and they have a high quality website that might be worth studying.

Best of luck from an aspiring board game designer!