By effectively (and affectingly) contrasting the beguiling, endearing beginning and the rancorous, soul-crushing end of a romantic relationship — and leaving out the tricky, complicated path that led the couple from A to Z — ‘Blue Valentine’ paints itself into a corner.

The highs and lows of the love affair between Dean (Ryan Gosling) and Cindy (Michelle Williams) are obvious  and devastating to contemplate. How could such a sweet couple descend into the depths of emotional pain that they eventually inflict upon one another? Yet without much insight or understanding of what, exactly, went wrong between the two, it’s difficult to muster up continued empathy for their situation, once the contrasting differences have been convincingly established through the use of extended flashbacks.

Yes, what happens is ugly and sad, but once we see where things are headed, we don’t really need to see events play out to the bitter end; we’re all too familiar with how things work out when two unhappy people are locked into a loveless union that cannot sustain itself. ‘Blue Valentine’ makes that point abundantly clear, and then makes it again and again. It could be argued that seeing things through to their conclusion is required for “closure,” but closure, at least for me, means more than merely seeing what happens; it involves some degree of understanding, and how things got that way, as well as a measure of forgiveness for one’s own faults and those of others involved.

We get none of that here. Once the point has been made, we’re just wallowing in current unhappiness and nostalgia for better times.

Or were they better? It could well be that the start of the relationship between Dean and Cindy fated them to a life of unhappiness as a couple. They both came from unhappy home lives: Cindy’s parents constantly bicker, and Dean’s mother abandoned him to his father years before. Unbeknown to Dean, Cindy had a boyfriend of sorts, a wrestler named Bobby (Mike Vogel), and so she was apparently cheating on Bobby when she began dating Dean. When she gets pregnant, it precipitates big decisions for the two of them.

It may well be that director Derek Cianfrance, who co-wrote the script with Joey Curtis and Cami Delavigne, intended to convey the idea that, no matter what, a relationship built without a solid foundation of mutual trust and understanding of each other’s emotional and physical needs will inevitably flounder.

If so, the willfully convoluted time-line makes it unnecessarily difficult and confusing to follow the arc of their relationship. Dean and Cindy slip into flashback mode at will — I didn’t even notice it at first, until I realized that “Old (Current) Dean” has a receding hairline and wears glasses. (Both “Old Dean” and “Young Dean” magically have the same amount of facial hair.) The film then slides back and forth, jumping from current events to different points in the initial courting stage of their relationship, providing apt commentary on what’s taking place in the present day. In their younger years, Dean and Cindy speak dreamily of idealistic love and career aspirations; in the present day, they snipe at one another, constantly pressing the hot buttons of the other.

Gosling and Williams are scarily accurate in their performances. They are very, very good at conveying the depth and range of feelings that exist between two people who have shared so much. Even so, ‘Blue Valentine’ is a frustrating, dreary, emotionally draining experience, a brutal — and not very edifying — way to spend nearly two hours locked in the private hell of two strangers.

‘Blue Valentine’ opens today at Landmark Magnolia.