I know there was some confusion as to the general storyline of Plush, but it looks like most sources are now claiming this as the official plot:

Plush is a story of rising rock star Hayley (Browning) who, after losing her band mate and brother to a drug overdose, finds herself in a downward spiral. The second album from her band Plush is received as a critical and commercial disaster, but she finds new hope and friendship in Enzo (Samuel), the replacement guitarist who inspires her to reach new creative heights. However, their collaboration soon crosses the line sexually and Hayley, not wanting to betray her husband (Gigandet), retreats from Enzo’s advances. As Hayley slowly discovers Enzo’s dark and troubled history, she realizes she may have let a madman into her home and family and that her mistake may cost the lives of people closest to her.