I'm not sure loneliness in sobriety is a secular thing so much as just a side effect of distancing yourself from your social circle of drinkers. After all many of us did everything drunk, and with other drunks. Sometimes as a survival mechanism you have to distance yourself from people that drink, especially in early sobriety. Of course, lots of people started drinking in the first place to deal with social anxiety. So take away the booze and the social anxiety remains.
A forum is not the same as having face-to-face friends but I find it incredibly valuable nonetheless.
I find one of the best ways to meet people is through hobbies. I've met quite a few people IRL that I got to know through forums dedicated to camping, hiking and the outdoors. A big advantage is that those places are full of people that will automatically have something in common with you. So that could be a book club, an amateur sports team, a knitting circle, a trap shooting league, etc.
Lastly I kind of like to hang out and surf the net at a favorite coffee shop. I can around other people while not really having to engage with them all.
Of course if you like that can lead to actually meeting other humans.
