The WSJ has a great article today about that most fickle and capricious of creatures, the Goldman Sachs investment banker. He’ll sidle smoothly up to you, buy you a drink at the bar, even get in to bed with you — but it’s not you he wants, he’s really only in it for the money. And if your rich uncle raises his eyebrow in a suggestive enough manner, your paramour is suited up and out the door faster than you can say “secrets of the boudoir.”

A few months ago, the spurned lover was J Crew. Goldman was dating J Crew if not quite going steady: “from time to time over the past several years,” the proxy statement says slightly wistfully, Goldman had “prepared various illustrative financial analyses for the Company.” Ah, those were the days. But sadly they came to an end: a commitment to J Crew would never last long, seeing as how the company was about to be sold. An engagement with the mighty Texas Pacific Group, by contrast, was likely to be a much more lucrative union over the long term. Especially when TPG didn’t just want Goldman’s confidential advice, but also wanted to delve deep into its debt-finance facilities.

But that was just a warm-up for Goldman’s latest show of caddishness. Last summer wireless networking company Clearwire tied the knot with Goldman in a formal ceremony which involved paying a substantial dowry. Yet mere months later, having gotten to know the most private and confidential secrets of Clearwire’s special board committee, Goldman formally transferred its affections to Clearwire’s more buxom step-sister, Sprint Nextel. Oh, the betrayal!

Clearwire’s directors, report Anupreeta Das and Gina Chon, are “upset” — and you can see why! Clearwire was what’s known as a “sell-side client” — one where investment-banking fees are pretty much guaranteed. No matter who ends up buying the company, its financial advisers end up getting paid. Buy-side mandates, by contrast, are much less certain affairs: if you lose the bidding, your client won’t pay you much. Or even anything at all, in many cases.

And like good-for-nothing scoundrels, Goldman’s has decided to go very quiet when called on its behavior. It declined to comment to the WSJ, but did let it be known that “Goldman lawyers reviewed the relationships” before signing off on the treachery.

As if that’s likely to make the Clearwire directors feel any better. And of course they can’t even get their own back. Goldman’s cunning that way: he’ll get you to confide all your deepest and most private secrets. But he’ll never reveal any of his own.

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Felix Salmon is an Audit contributor. He's also the finance blogger for Reuters; this post can also be found at Reuters.com.