I also feel like I've struggled to meet people I 'click' with as an adult despite having had lots of friends when younger.
I still have 5/6 friends from school (I'm now mid-30s) but none of them live locally. I probably see each of them a couple of times a year max. Still get on ok when we do meet up but our meet ups are becoming fewer and further between as people get married and have kids.
I work in the City & have a few 'London' friends who are more acquaintances really, who I go for occasional dinner or drinks with, but I wouldn't phone them for a chat or anything. And if I stopped working in London (which I plan to do one day) I doubt I would see them anymore.
There's various other people I've met over the years who I'm semi-in touch with, as in connected on Facebook and I might drop them a message if I happened to be passing through where they live on my travels, but I don't see them regularly and I wouldn't make a special effort to visit.
I've lived in my current town for around 5 years and have no friends. I'm slightly friendly with one neighbour but she's running around after her kids (I'm childfree) so we don't see each other often. But I could call her if my boiler packed up and I needed a hot shower!
I'd like to meet a couple of local friends but my efforts have all been in vain. I often just don't think people take to me 
I do like my own company though, and DH too. I also have lots of hobbies and work full time so I'm rarerly at a loose end.
I've met random people I chat to through my hobbies but no one I would call a friend yet.
I am sometimes lonely.