A part of your humanity dies when you forget you can always lose everything, find yourself in line at the soup kitchen or on the business end of a crack pipe and your teeth falling into your hands. Child Protective Services used to tell trainees stories of horrific abuse they’d be likely to encounter and then asked them if they could ever see themselves at a place in their lives where they’d act like the parents in question. If you raised your hand, you were missing the point.

“Grey Gardens” is a story about abuse, and fragility, and riches to rags, of how even Jackie Kennedy’s East Hamptons cousin and aunt turned into cat lady recluses, going to the bathroom on the floor amid cats and raccoons and roaring 20s finery once the men departed and the money ran out.

It’s arguably Drew Barrymore’s best performance, as the younger of the two (Jessica Lange plays her mother with batty, needy precision). Barrymore’s crack-up — from aching-for-attention beauty Little Edie in pre-War New York — is heartbreaking, especially because it’s her mother who hands down the life sentence.

It’s a phenomenal movie, but it’s off the mark to call it, as some have, a “love story.” You wouldn’t use the word “luck” to describe “bad luck.” Little Edie is a prisoner. When finances look like they’re drying up and the two talk of moving, to a cheap, sunny island, and Little Edie murmurs, “I could travel, maybe meet someone,” you can see her mother mentally destroy the idea like a bug. Her mother is a black hole, from which no light can escape. Their love for each other is desperate dysfunction — bad love. And that kind of love’s no love at all.