Sex addiction can be a subject for drama (Shame) or a comedy with dramatic undertones. That would be Thanks for Sharing, starring Mark Ruffalo, a fine actor in rare form, as Adam, who’s in a 12-step program to stop fucking everything that moves. He’s been five years keeping it in his pants. He has help from Mike (Tim Robbins), his sponsor in the program, but trouble erupts when he tries to have a serious relationship with a woman (Gwyneth Paltrow) and must tell her his history. Ruffalo and Paltrow do a good job pretending this relationship isn’t a contrivance. Screenwriter Stuart Blumberg (take a bow for The Kids Are All Right), in his directing debut, struggles with these scenes. What works, gloriously, are the therapy sessions, which include Josh Gad as a jerk-off king and, best of all, Alecia Moore, a.k.a. Pink, who steals every scene she’s in as Dede, a sex addict struggling to understand her dysfunction. It’s serious business and serious fun watching her try. Thanks for Sharing is all over the place trying to find a tone, but it knows where its heart is.