I think the whole murder thing is a metaphor. She swore to never leave him but does anyways. "She lies and whispers loving words" might mean that when leaving him she keeps telling him she loves him, which would be a lie. And the line "A kiss will end his pain and she drives the blade..." bassicly is saying if she would just show her love to him, he would be ok, but instead she drives in the blade...the pain she causes him
I think the whole murder thing is a metaphor. She swore to never leave him but does anyways. "She lies and whispers loving words" might mean that when leaving him she keeps telling him she loves him, which would be a lie. And the line "A kiss will end his pain and she drives the blade..." bassicly is saying if she would just show her love to him, he would be ok, but instead she drives in the blade...the pain she causes him