Quads don't seem to be as common a configuration, but there are a few members here who are in successful quad relationships. I'm pretty sure there was a recent post by someone who cohabits with their quad. And there is one member here who was posting a lot for a while about how happy he is in his quad, enough that I recall suggesting he write a book about it! Not enough info out there on quads. Do a "Tag Search" or "Advanced Search" here for "Quad" or "Quads" and you should find some discussion threads.
The world opens up... when you do.
Oh, oh, can't you see? Love is the drug for me. ~Bryan Ferry
"Love is that condition in which another person's happiness is essential to your own." ~Robert Heinlein