DEAR SUSAN: Last weekend, I had sex with a girl who's just a friend. She and I laughed and said it was friendship with benefits. But now she's calling me regularly, asking when I'm coming to see her again. I feel so guilty. But it was purely platonic on my part. She's a nice girl, but honestly, it meant nothing. — From the "Single File" blog

DEAR BLOGGER: But it could have unlocked some hopes in her. (Deep sigh.) That's the tricky part of this misnomer; it's supposedly "casual" but rarely so. The hurtful part of the rutting we've come to label casual is that one of the partners usually brings into the bed a secret hope. That person doesn't dare express it, fearing the other will fly the coop. So the hopeful partner plays the game, pretending the passion is the only thing shared, but what lies beneath is a yearning for the real thing. And if you suspect the pretender is usually female, you are correct. She is often the one who secretly harbors that yearning. So the path of casual sex is littered with feminine yearning. The female of the species is the one who proves that casual sex is an oxymoron. How can the joining of pulsing flesh be ho-hum casual? Think about it. Then call her and apologize.

DEAR SUSAN: I did it. I moved in with the girl of my dreams, but it turned out to be a nightmare. She became a CEO like her father — and acted like a CEO, giving me orders and scheduling everything from laundry to sex. It took a while for me to wake up and do something about it, but I believe more than ever in living together as a test run. — From the "Single File" blog

DEAR BLOGGER: Join the club. I've seen and read much too much to deny the good sense of a compatibility test. There's nothing like boots on the ground to sample what lifetime love feels like with a certain someone. But on the other hand, you can't make a lifestyle out of three- or four-month compatibility tests. Besides, you know pretty quickly how it feels to be with the person, alone in your own hacienda.

After this horror, you'll see how finely tuned your senses become to habits and attitudes; it won't take you very long to get the "feel" of a person. And if the someone is malleable, she will be glad for your comments — as you will be for hers. (Ahem.) The more throughput in your dating life the quicker the verdict on someone's eligibility as a housemate. You'll develop that "feel," a subtle but unmistakable sense of the person's modus operandi. And as your knowledge about people and their habits becomes more sophisticated, testing for compatibility becomes less and less necessary.

Have a question for Susan? You can reach her directly at susan@single-file.com.