And so the parable of the unpopped cherry goes on … and on. The epic of the unbroken duck continues. As the final whistle blows on the third Eclipse movie, after more than two hours, with still nothing on the scoreboard, virginal high-school teen Bella Swan is starting to make Doris Day look like the nympho from hell.

Bella (Kristen Stewart) is still deeply in love with dreamboat vampire Edward Cullen, played by Robert Pattinson, who has unattractive sideburns, beige contact lenses and increasingly quiffy hair, like some sort of diffident, undead Elvis. But she, of course, is also being courted by a werewolf hunk called Jacob, played by Taylor Lautner, a reckless, shirtless individual who has fallen for her. Both Edward and Jacob are gallant enough to realise that pressing their physical attentions on Bella means her having to relinquish human identity and commit. And there is no question of any noisome compromise, such as that by which ex-President Clinton technically avoided "relations" with Monica Lewinsky. So far, Bella has been reluctant to take the momentous step, but she certainly likes Edward more than Jacob.

As the film starts, the idea seems to be that she will make Edward wait only as far as her high-school graduation. But then things change. Edward proposes marriage and so the moment is deferred. Now he will wait until they are actually Mr and Mrs Cullen. Who knows if there won't be many other excuses to put off the evil hour? Perhaps she will make Edward wait until she's left college, until she's finished grad school, until she's had her bar exam, or until he's had his first prostate exam. Or perhaps she will relent and give him a portion at some stage in the fourth and fifth Twilight movies: Breaking Dawn Part One (expected 2011) and Breaking Dawn Part Two (expected 2012). I only hope that these people's expectation of their first experience has not become unrealistically high. In the meantime, Bella's L-plates seem to be pretty much welded to her moped – and I moreover wonder if there isn't another undercurrent of emotion flowing here.

The latest crisis in Bella's emotional and non-sexual life happens to coincide with a terrible situation in Seattle. A grotesque serial killer is reportedly laying waste to the local population: news that Bella's divorced cop dad monitors by idly reading the headlines in the local paper, while perhaps sipping a frosty one from the fridge. We see one empty can on the coffee table, denoting that he is lonely, but not excessively so.

But we know that the culprit is not homo sapiens, as such. A crew of "newborn" vampires is running wild, under the influence of the red-haired Victoria (now played by Bryce Dallas Howard), who is out for revenge after Edward killed her lover, James, in the previous movie. This awful new bunch of vampires is thirsting to destroy Bella. So the vampires and the werewolves, Team Edward and Team Jacob, have to team up to see off the intruders and protect Bella.

There is an arresting scene in which, having used Bella's scent to lure the newborns to a certain stategically advantageous part of the forest for a showdown, Jacob has to carry her around the woods in his hunky arms to mask her musk – I think – and Bella snuggles coyly in his stern embrace. This looks like yet another excuse for non-sex contact.

It has become a truism to notice that the romance of vampires and other creatures in the Twilight books and movies is a metaphor for abstinence and denial. Over and over again, Edward and Jacob square up; over and over again, they find themselves smouldering at each other, at close quarters. Somehow, they find themselves camping out on the remote mountain, all three of them sharing a tent, and while Bella demurely gets some sleep, these two alpha males yet again face off, taunting each other. "I really get under that ice-cold skin of yours, don't I?" breathes Jacob. "If we weren't natural enemies, I might actually like you," murmurs Edward.

Oh my lordy, you could cut the tension with a knife. Later, Jacob discovers that Edward is engaged to be married to Bella, and he is really upset, and the audience is entitled to wonder if his state of mind isn't cloudier than it at first appears. If E Annie Proulx and Larry McMurtry were writing this, Jacob might have to go away and get some unsatisfying cowpoke job after he came down off the mountain, while Edward works in Bella's father's farm machinery business. As it is, they struggle on in the roles society has laid down for them. This vampire tale was a refreshing novelty in the first film: with the fourth and fifth now on the way, it could be time to sharpen the wooden stake.