Celeb fotog Steven Meisel has slapped his ex-lover with a lawsuit for allegedly running up a huge AmEx tab on romps with male escorts in LA and Vegas. Meisel, 60, whose portfolio ranges from racy shots of Madonna for her 1992 book “Sex” to spreads in Vogue of Naomi Campbell and Christy Turlington, says longtime beau Benjamin Forest has been mooching off him and living in his $13 million Beverly Hills mansion since the two split in 2010. Meisel paints his estranged boyfriend as a drug fiend, “who has been using, and continues to use illegal drugs.” He wants the court to rule that Forest has no legal claim to his real estate. Forest hung up on a Post reporter asking about the allegations.