Howard Jacobson: Our dark side is closer than we think

Exhilaration can turn to ashes in the beat of a heart. Build this knowledge into your expectations

Ever heard of the expression "cranking"? I encountered it for the first time only a couple of days ago.

Apparently it means crying while you're masturbating. Myself I'm surprised to discover there's any other way of doing it. Masturbating is the saddest thing a person ever does and tears are its only rational accompaniment.

So why, I'm wondering, does one need a special term for it? If you want a special term, reserve it for the act of not crying while you're masturbating. Or laughing while you're masturbating, which could be construed as an ethical act. Or just not masturbating at all, which is the noblest way of the lot. Of the moral crimes committed by the 20th century, the removal of stigma from self-pleasuring will one day be counted as among the greatest. Reader, we were a more serious species when we believed we would go blind. Which was only ever a metaphor anyway. Like hairy hands. We go on taking an interest in men turning into werewolves, or Dr Jekyll morphing into Mr Hyde, but the figurative meaning of hairy hands still escapes us.

But back to "cranking". Just possibly, the person I heard talking about it – the actor Ryan Gosling – was having a joke at his interviewer's expense. Such clowning would be of a piece with his performance in Blue Valentine, the best movie about men and women – just that: men and women and why they fall in love and then out of it – I've seen in a long time. That it was pretty well overlooked in all categories by the Golden Globes, and again by the Baftas – and this in a year when people are falling over themselves to praise Black Swan, which is grand-guignol gothic tosh from start to finish – shows how hard it is to get notice for a movie which deals with sex in an adult way. Same, of course, with novels. Depart from the sticky-sweets of love when you're describing satisfaction, or melodrama when you're describing its opposite, and no one knows where to look. We will countenance any subject today except eroticism – unless the eroticism is normalised into romantic comedy, as in Meg Ryan's faking it in When Harry Met Sally, or made ludicrous with exhortations to find your "dark side", as in Black Swan.

The truth about the dark side is that you don't have to work very hard to find it. It will come to you when it's good and ready. Now it's in operation, now it isn't. Just like your light side. The tragic part being that what sex wants of you isn't always what you want of yourself, and can be further still from what your lover's hoping for. Those lovers are lucky indeed between whom, like Shakespeare's phoenix and turtle, no division exists.

Ryan Gosling plays a nice guy in Blue Valentine. Ordinary in his domestic ambitions, but extraordinary in the sincerity and persistence with which he pursues them. He is a thing almost entirely of emotion. The film opens with him playing with a child who turns out not to be his, though we wouldn't know that from his devotion to her. That he has the time to play, as a guy who does a bit of this and a bit of that, while his wife has a job to go to and wants the child dressed and ready for school, ought not to count against him. Our daughters should be so lucky as to find so sweet a husband. It shouldn't count against the woman either that she is a mite tetchier and less playful than he is. She's the breadwinner. She has things to worry about that he won't. And anyway, play is man's reserve. That's what men are put on earth to do. (I have a theory about this. Play originates with the penis. No penis, no great instinct for piddling about. But I don't want to embark upon a course which as sure as eggs are eggs will lead us back to "cranking".)

That no one is necessarily to blame, that tensions will arise because they will, that destruction is intrinsic to a sexual relationship, which remains a sexual relationship even when the sex is dormant – these are the painful and perplexing truths from which Blue Valentine never flinches. In one scene the husband takes the wife away for a night at a themed hotel. He wants a night of passion. She does not. He sees her in the shower. He is aroused. You can't see the woman you love in a shower and not climb in to help her with the sponge. But for her a shower is a shower. She is away from home. She would like to luxuriate a while on her own. Who's to blame? He could have been more sensitive to her mood. She could have been more sensitive to his. Hotel showers do this. They set lovers apart. Everything sets lovers apart. Love sets lovers apart.

But it also brings them together again. They try out old patterns. In one excruciating scene they imitate themselves as they once were. It doesn't quite work but it nearly does. Nearly should be enough. What's wrong with nearly, for God's sake. But love is forever dissatisfied. The night wears on. They drink. Something close to intense sexual passion reignites itself. They make love, but in a way that neither of them feels is quite right. It turns a little violent. Does she want violent? She doesn't know. But maybe she will try it. Does he want violent? He too doesn't know. He tries. He doesn't. He is a manly but sentimental man and doesn't recognise himself even in the act of pretending to cause pain. What has quite happened neither of them knows. Michelle Williams plays the wife to Gosling's husband. You will go a long way to see two more emotionally intelligent performances. As young lovers they are – I don't mind showing my softer side to say – bewitching; as a pair who have gone adrift, they break the heart.

I'm not sure where sex education has got to now, but I'd recommend that any person old enough to be told what goes where should see this film. Not because it depresses hope but because it teaches humanity. There is no right or wrong way. Most times there are no villains. Sorrow is built into sex and vexation into love. Marriage can be sweet one moment, vile the next. Exhilaration can turn to ashes in the beat of a heart. Build this knowledge into your expectations. Refuse the false optimism of the woman's magazine. And trust neither Golden Globe nor Bafta.