I have two groups of closest friends. My friends from school, there's a group of 6 of us and we're still best friends.
Then there's my group of friends from uni; my husband and some of his friends from school came to uni together. Others of us joined this group, plus their other school friends went to uni's not so far away and used to come for nights out a lot. We became one big group of friends, like 25-30 of us and continued after we graduated, most of us lived and worked in London (and still do). Eventually many of us married within the group haha but those who married outside of the group, their other halves also joined the group. So we're all still a big group of friends and the wives are best friends and the husbands are best friends.
I've even managed to combine my two groups, since my husband and I set up our uni friend up with my school friend. They got together at our wedding and are now married! They also lived with us for a bit a couple years ago.. It's been fun haha. We had like 4-5 years of 4-5 weddings per summer, our weddings were the best (we're all Indian, 20 Indian weddings + 20 hens/stags = immense fun)!
We're all basically married & in our early 30's now. Some have moved abroad (including myself, but back in London now) and babies are entering the scene but we all stay in touch. We have various WhatsApp groups where we speak probably daily, and we still socialise as smaller groups within the group on a fortnightly-or-so basis? We usually only meet up now as the whole group on people's birthdays, as nowadays it's difficult to schedule so many people, but we have like 15 of those a year too. We've basically grown up together, and I'm looking forward to the next stage of our lives & hopefully watching our kids grow up together.. :)
In the words of Phil & Kirstie, its all about location, location, location. I think living & working in London definitely made the difference. We used to go out drinking every Thursday/Friday in Central after work, this is also how some of the couples happened haha. Also since a lot of the boys and a couple of the girls went to school together, when they lived with their parents after uni they were all local to each other. For those who didn't, these guys were our bf's so we were also around a lot. It was all a bit incestuous but I guess that's the key!