Dear Carolyn: I am a 21-year-old guy, who, admittedly, is in love with being single. Since my last relationship took a turn for the worst after being the most serious relationship I've ever had, I am better off finding my inner self and enjoying time with the friends I had let slip. However, and this may sound very bad, I do miss the sex. I called an old ''friend'' in order to basically arrange for some good old-fashioned casual college sex over drinks at my place. It quickly turned kinky, and now, over two weeks later, this girl will not leave me alone. I haven't written off becoming involved with someone at this point, but it would have to be just right. This girl wasn't even a little right. She was definitely Ms. 100 Percent Wrong. I regret what we did, but I think she probably has developed feelings for me and I cannot even begin to describe my lack of interest for her - not even for any more hookups. I just flat-out don't want to see her at all. Nonetheless, she hasn't ceased calling me incessantly day and night. I want to do right by this, Carolyn, but frankly I don't know how.

- I Need Advice

Dear Advice: What are the chances you could have developed feelings for her during one night of kasual kinky kollege sex over kocktails?

Right. Well, those are roughly the same chances that she's developed feelings for you. Men and women may be wired differently, but not so differently that the laws of emotional physics no longer apply.

Since the first step in fixing a problem is to know what the problem is, please realize her desperate calls don't mean she's desperate for you.

What is she desperate for? I could be wrong, but:

You describe an evening that ''may sound very bad'' and apparently got out of hand, which you now regret. Dirty boy, right?

Now put yourself in her place. Women who indulge their ''very bad'' needs are, in general, denied the nudge-and-wink, dirty-boy treatment. Dirty girls are slutty, disposable, used.

Aw-shucks regret, vs. hate yourself regret.

This isn't a men-are-pigs rant, it's just an ''is''; society judges women more harshly. Some women are fine with that, some aren't, some think they are but find out the hard way they aren't. Sounds like you called a girl from Group 3.

So, what now? Whether I'm right or wrong here, you owe her more than the voice mail void. (Just as you owed her complete honesty when you initially called her for sex, a standard to which I'm guessing you ''basically'' fell short.)

Call her. Apologize for not being clear enough about your motives - even if you were. Say you thought she wanted casual sex, too, because you never thought she had feelings for you; truth and humility make a fine pair.

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Carolyn Hax's column runs Mondays, Wednesdays and Fridays. You can e-mail Carolyn at tellme@washpost.com or write: ''Tell Me About It,'' c/o The Washington Post, Style Plus, 1150 15th St., NW, Washington, D.C. 20071.