Mario died from a heart attack in front of Marco.
Not exactly. She had self esteem problems and she was browsing at a department store. Talbot offered her sex in exchange for the dress. The euphoria elevated spirits and then he started to introduce her to other men. Over time, it became an addiction. Then Marco found out and blackmailed her into being his "Madam". The fitness club, I believe, was a front for a whorehouse.