I feel like the line "If you can keep a secret, I can keep a secret" might be sarcastic...perhaps it's stating that since she kept the secret that she was cheating on him, now he's keeping the secret of her murder.
I feel like the line "If you can keep a secret, I can keep a secret" might be sarcastic...perhaps it's stating that since she kept the secret that she was cheating on him, now he's keeping the secret of her murder.