This is an excellent example of a dramatic monologue in which Carol Ann Duffy breathes life into one of the most fascinating and mysterious characters in Dickensian literature: Miss Havisham from Great Expectations by Charles Dickens. She is famous for responding to being jilted on her wedding day by trying to freeze time, wearing her wedding dress and letting the wedding feast rot in front of her for the rest of her days.
In this poem, therefore, there is a curious mix of love and hatred, signified by the opening sentence: "Beloved sweetheart bastard." This paradox identifies her confused emotions as her hatred against her former lover is welded to her love for him in a confusing mix of emotions. She goes on to personify herself as "Love's / hate behind a white veil" which again picks up on this contradictory emotion.
In a sense, we could argue that Miss Havisham, though still alive, begins a living death from the moment she is jilted. Note how the second stanza describes the pitiful life she leads:
Spinster. I stink and remember. Whole days
in bed cawing Nooooo at the wall; the dress
yellowing, trembling if I open the wardrobe...
Such descriptions focus on the insane-like state that Miss Havisham enters because of her pain at being jilted and presents us with a woman who is tortured by what has happened to her and is only able to find temporary relief in the dreams she has of being united (sexually?) with the man who jilted her.
The last two lines bring the themes of love and death together in a stunning ending:
Give me a male corpse for a long slow honeymoon.
Don't think it's only the heart that b-b-b-breaks.
On the one hand, her love is shown by the way that the last line clearly indicates Miss Havisham is heartbroken. On the other hand, she desires the death of her former lover for her "long slow honeymoon," grimly subverting the normal expectations of honeymoon so that in death she can get her revenge. The stutter on the word "b-b-b-breaks" also clearly suggests that it is more than Miss Havisham's heart that is just broken, as she perhaps slips into obsessional madness.