a forum to commiserate and share advice and coping mechanisms and so on.
Speaking for myself here, but I feel like this can make the problem worse. /r/depression is something in a similar vein. Whenever I went there, I'd always leave sadder. There's something about reading other people's struggles that just seemed to reinforce my own sense of hopelessness.
Also, bad advice on those kinds of forums can look extremely reasonable if your perception of the world is clouded by your problems.
I know it doesn't work for everyone, but give therapy a shot if you haven't already.
Like others have said, having a friend that you see regularly can help with loneliness. Doesn't even have to be strangers. Try messaging an old friend you drifted apart from. Odds are they'd be happy to catch up.
Sorry for the unsolicited advice. I know this isn't the type of response you asked for. I hope everything works out for you, bud.