I’m just wondering if these women were actually friends at all? They sound more like acquaintances who you’ve shared social events with, is that so?

In which case it might be that they have more in common with your girlfriend and so have more of a genuine bond with her?

Personally I’d be looking at accepting the situation, some people just naturally gel together, especially as they’re all women. They probably still like you just don’t gel with you in the same way. That doesn’t mean you won’t find other people to socialise with who you gel with more.