My situation isn't wholly unlike yours, with the move-in and love and fooling around and crazy... Yeah.
Two years ago, my boyfriend--now fiance-- and I moved in with a couple of friends to save on rent in a new city (and because I believe in cohousing, and we lived together in college dorms, and...).
Another friend wanted to move in with us, and started fooling around with me after plans had been made. We were both taken by surprise, but really pleased. Things progressed wonderfully, albeit rapidly, and I call him my partner now.
Then we moved into a bigger house, with more friends. Then I started dating an ex-girlfriend again (long-distance), and when she came to visit she fell for a housemate. She's moving in with us soon, and so is another good friend of mine (we're now in the "-with-benefits" category), and so is an ex-boyfriend who is likely to become entangled again...
There's almost a dozen of us in the house these days, and we're not all dating or fooling around or whatever.
So yeah-- poly cohabitation complications. It's not just you!
"I was thorough when I looked for you, and I feel justified lying in your arms." - Chasing Amy