Their troubles were tabloid fodder and their relationship seemed to outsiders to be a mismatch. But for 14 years, Whitney Houston and Bobby Brown publicly professed their love for one another. The couple’s tumultuous marriage appears to be coming to an end. Houston filed papers in Orange County Superior Court yesterday requesting a legal separation from Brown because of irreconcilable differences. Houston’s publicist, Nancy Seltzer, said the Grammy-winning singer would have no comment on the action.“It is a legal separation. It is not a divorce or a divorce petition,” said Phaedra Parks, an entertainment lawyer who represents Brown. Houston, 43, asked that she be granted custody of the couple’s 13-year-old daughter, Bobbi Kristina, and that Brown, 37, be allowed visitation rights. She asked that property rights be determined later.When the couple wed in 1992, Houston was one of the best-selling singers in history and was a glamorous, pop superstar with a super-clean, princess-like persona. Brown, on the other hand was a coarse R&B singer with a more street-wise image after rising to fame as a member of the boy band New Edition.