Ryan Murphy (Michael Loccisano/GETTY IMAGES FOR MICHAEL KORS)

Roberts, who was last directed by Murphy in the best-forgotten “Eat Pray Love,” will play Emma Brookner, a physician who treated some of the earliest HIV/AIDS patients in New York in the early ’80s. Ruffalo will take the role of Ned Weeks, the founder of a prominent HIV advocacy group. Bomer has been cast as the reporter who became his lover.

The project, which was knocking around last year, won’t be seen until 2014, HBO announced.