Un-dear Diary: Well acted, directed, written but a hard movie to like

The Diary of a Teenage Girl (Marielle Heller, 2015) starts out looking (and feeling) like a sweet coming-of-age story set in 1970s San Francisco and narrated, into a cassette player, by a somewhat awkward, artistic 15-year-old (Bel Powley). Pretty quickly, though, the movie becomes something else entirely, as the teen gets involved in an aggressive sexual relationship with her mother's boyfriend, a 35-year-old ne'er-do-well who of course is a loathsome predator and ought to be sent to jail for what he does to this vulnerable young woman. Over the course of the movie we watch the sad and pathetic descent of this young woman into a dangerous, sordid, and lonely life - entirely ignored by her drug-addled, incompetent mother (Kristen Wiig) and with no support from any source: her one girlfriend is completely unreliable and a terrible influence, she has no good relationships with boys, teachers, mentors, her stepfather tries to help a little bit but manages just to make matters worse, and when at last her mother learns of the completely inappropriate and in fact illegal relationship she turns against her daughter. Based on a novel (not a true story I hope and trust - most likely a YA book), this movie takes an inevitable downward course and then [ possible spoilers ] at the end picks up in an unlikely fashion as the teen finds some salvation in her artwork (Heller incorporates some imaginative computer-graphic illustrations to highlight certain moods and moments throughout the film) and as her mother at last comes to her defense, at least a little, and she bonds with her largely ignored precocious younger sister. Powley plays the part very well, and the movie is sure-handed in achieving the effects it wants - and does a great job of putting this poor girl's troubled life in the context of what I can only call the loose morals of the era, very troubling for a girl without help from family or friends or school), but despite the limp attempt at an upbeat ending it's hard to imagine anyone actually liking this film. Personally, I'd have liked to see the Lothario hauled off in chains, but the movie leaves him alone and unscathed, which is probably a realistic ending sad to say.