Teachers are the worst, when it comes to this stuff at work. It's a hazard, I'd say of being a female dominated profession. The mean girls rule.
However, I'd say that while I was part of a group in my last teaching job, it was based on work stuff. And, in middle schools, you work on a team, and that bond can be very strong. What got to me was teachers constantly complaining about their husbands and how stressed they were from their kids. Once in awhile I would pipe in and say, "My husband does not do that." I stopped socializing with work people long ago.
I am very social and have had several groups through out my life. But I have found the principle of "friendly, not friends," (which I used to teach my students, so they could tolerate working with others) needs to be applied at work. One of the reasons I like working in my clinic is that I don't have to socialize with anyone. I meet with my supervisor 1X a week and I casually talk to other therapists. But, I could come in and shut my door and never talk to anyone, if I wanted to. The other therapists are nice and we actually have stuff in common, but I am not going to pursue friendships there.
I am still pretty upset about our friends moving to Amherst. I get very bored without social plans and our other friends are more the just go out to dinner types. Over the years, our commonalities have diminished. I had a huge group of friends as a kid, a group of 5 close friends in HS, and tons of acquaintances, before I moved. I was active in student government and spent my childhood roaming the streets of my neighborhood with a huge group of kids, on my bike. While I do spend the majority of time with my DH, sometimes that gets on my nerves and makes me feel isolated. I even feel antsy at night, because after teaching for so long, I still am not used to not having tons of work to do when I get home. Last night, I said I was bored, and DH told me I was nuts! I'd say one of the only downsides of moving back to MA was that too many people here just hang out with their families, because a lot of them never moved away. Always obligations with parents, siblings, extended families. In AZ my friends were our family, and everyone was in the same boat.