An observation about the couple
I sense Amy was perhaps not really into men, she struck me as possibly a Lesbian. Her behavior towards her husband and former boyfriend was not only criminal but there was an undertone of disinterest in the male species as a whole. Which could explain why they were so easily disposable to her in terms of their lives (killed one and almost had the other executed).
Nick strikes me as the type of guy who genuinely wanted to be child free and was regretful of married life. Despite his assertions of ''wanting kids'' I don't think he did and I don't think he was ever in love with Amy. The marriage was perhaps faulty from the start. He wanted to date, he didn't want a wife.