Ending?

Basically she wants to ease his pain but also her own. He's on death row with no future except his execution imminent, while she's living in an unhappy marriage with his cheating spouse. Through sex they experience intimacy and seek renewal. The important part is when she blocks his nose and mouth so he can't breath except through her - if she breathes. If you watch the scene closely, you'll notice that she alternately breathes (almost desperately) and doesn't breath at all. It's like artificial respiration that she may have needed when she nearly drowned as a kid. They share a moment of life and death.

For him it seems to mean that he's able to come to terms with his imminent death: he's crying and doesn't try to fight when the other obviously homosexual inmate who has feelings towards him (and is jealous of his relationship with her) is strangling him. Ironically in both drowning and strangling the cause of death is suffocation. (However I don't think he kills him because when he stops strangling he closes his eyes.) She on the other hand seems to get over her unhappiness. His spouse stops cheating on her and they bond again; the family plays together in snow and on their way home first she sings alone, then he alone in response and finally they sing together.

I think the ending is very important to the film. I wasn't awfully excited about the film before the ending but it made me appreciate the film more.

I understand the ending, but it sucks. The movie was awesome, but the ending is a big anticlimax. He SHOULD have died at the time when they were having sex and she closed his nose. That way, he no longer had to fear dying and had a beautifull death in the arms of his loved one. This would have been a great gift of her towards him. (Anyway, it beats the electric chair or the bullet!)
Just my 2 cents.