Workplace relationships are going to happen, no matter what. And when they do — and then fall apart — HR pros probably shouldn’t use this story as a guide on how to handle things.  
Melissa Gerald was a scientist with the University of Puerto Rico. Her supervisor was Edmundo Kraiselburd.
After working together for several years without incident, Gerald and Kraiselburd engaged in a weeklong sexual affair at a conference in Cuba.
When they returned home, Gerald, who was embarrassed by the fling, rebuffed Kraiselburd.
Several years passed without incident, until one night when Kraiselburd propositioned Gerald for sex after a work dinner. Gerald refused, upsetting Kraiselburd.
The next month, after a meeting in Kraiselburd’s office, Kraiselburd grabbed Gerald’s breast and made sexually suggestive grunting noises.
The issues continued the following week during a meeting when Kraiselburd asked Gerald in front of a number of colleagues, “What will it take for you to f–k me?”
Not surprisingly, Gerald filed a sexual harassment complaint with her employer. The university interviewed a number of Gerald’s and Kraiselburd’s co-workers, and they all said that Kraiselburd and Gerald had a relationship that frequently included off-color remarks and jokes of a sexual nature.
After an investigation, the university determined that the first two incidents, which supposedly occurred in private, didn’t occur, and the third incident was called a common occurrence between the two colleagues.
All three were deemed “not severe or offensive enough to alter Gerald’s work conditions.”

Court disagrees with university

So Gerald filed a sexual harassment claim against the university.
A district court dismissed the case, but an appeals court sent the case to trial, noting:

“[The university] primarily argued that Gerald’s own conduct, namely her voluntarily engaging in off-color banter of a sexual nature with Kraiselburd, showed that his conduct was not unwelcome. This argument does little to convince. We fail to see how an employee telling risqué jokes means that she is amenable to being groped at work. Instead the evidence here was enough, at the very least, to raise a factual question as to whether Kraiselburd’s conduct was unwelcome.”

Now the case has been sent to a jury, and you know what that means — a lengthy trial or an expensive settlement.
The case is Gerald v. University of Puerto Rico.