>>33898373 (OP)
It's one the reddest of red flags.
Girls are social by nature and they want their boyfriend to be someone fun that they can show off to their friends group and social circles and not be a guy who's going to quietly stare at his feet the whole time.
Likewise, they want to be paraded around your own social circles and friends group as The Girlfriend, maybe they'll try to set up their fat friend with your ugly friend, etc.
Some girls didn't immediately lose interest, they stuck around for quite a while, and others totally did ASAP and would tell me to my face "you're boring and have no life (and you just want to have sex)"
which is half true, I just prefer staying in with comfy movies, which just so happens to lead to sex most of the time.
Also even the most anti-social outcast female epic nerd will still have like a half dozen people she always hangs out with every weekend, but they and others can accept that some guys truely are literal loners and that they're okay with it.
Anyways, having friends and social circles not only helps keeping the gf you get but it also helps you in a bunch of different ways of potentially meeting your gf to being with.