Complex sentence: She becomes entangled in a passionate affair with Linda, a makeup artist, but Linda begins to worry about Gia's drug use she gives her an ultimatum, and Gia chooses the drugs.
Split into simpler sentences: She becomes entangled in a passionate affair with Linda, a make-up artist. However, after a while Linda begins to worry about Gia's drug use and gives Gia an ultimatum, with Gia choosing the drugs.