Minecraft's always been a place to go when I want to be alone for a little while, so playing on a server has always been a little uncomfortable to me.
I've had other places that I'd go for companionship that cleared out over time, so while it wasn't Minecraft, I can imagine some of how you feel about it :-/
This comes from the fact that I run a server which used to have ~20 on at any given time and now has 0, along with the fact that I learned to play it alongside my ex-girlfriend.
I wish there was some way for me to get past the loneliness.