No real advice to offer because I seem to be much the same. That's despite having lived in the same smallish town in the UK for over 40 years. In the beginning, having small children brought me most of my friends, as did joining the PTA and being involved in several local things. Once they were at secondary school I went back to work full-time and I rarely had time to socialise. The final full-time job I had was 45 miles from home and apart from not being around to socialise with my workmates I fell out of the habit of keeping up other than a handful of friendships locally, similarly with friends who moved away. Sad to say, somewhere along the line I seemed to upset a few "close" friends, but despite asking them (and others) for a reason, none was ever forthcoming. I tried inviting them to things but they always declined.
I took early retirement 15 years ago age 59 after caring for my mum with dementia who died, and threw myself into local politics and my U3A, but despite people being friendly none have wanted to get any closer. Of course, I've also lost the few friends I kept to either dementia or death and now feel I've got almost no-one to call a friend. For the past six months I've been going through cancer treatment and though people know about it hardly anyone has enquired how I am doing, let alone offered any help.
I'm lucky to have two wonderful daughters but they are both busy with their own lives (and one is 200 miles away).
Then again, most of the people I meet nowadays are widows and widowers and I am still with my husband of 5 years, so maybe that makes a difference.
No idea what the solution is, but I do feel lonely a lot of the time.