The song is about the, now famous, 'love me or die' spell. Although this is a work that miss cat teaches, it isn't a spell I personally would make use of. It basically places a curse on the target, which causes them to slowly sicken unless they return to the lover and love them (or die). If they leave again they begin to waste away once more. The spell needs to be maintained to ensure the person stays alive, for the rest of their days. Probably not something you want to throw at someone you really love these days... so I won't describe how you do it.
Makes for a fabulous, atmospheric song though!
Now, certain idealistic people might say that such a spell should never have been conceived at all - but probably this has to do the social and economic vulnerability of women and their dependancy on men to provide for their family back in the day. To a woman with children, a man running away with another woman might well have meant much more hardship than a simple broken heart. So it's good to see this kind of spell in its right historical context before making sweeping judgements about its morality.
Naturally, these days some women (and men) get desperate enough in love that they might actually try this spell anyway. Let me just say - sometimes its easier to throw a spell than it is to undo it.
Sometimes you have to lie in the bed you've made.... or more precisely someone else might have to lie in the bed you make for them.
A hospital bed.