Are you talking about "Post Blue"? "to break the back of something" = to end the domination of something; to reduce the power of something. Anyway my interpretation is : I'll destroy my love for you ciao

Placebo's Post Blue lyrics "I'd break the back of love for you " sounds like he wants to make it easier for whoever he's had the affair with, to love him. The rest of the song implies there' s something between them they can' t avoid, like its part of their nature, and he wants to make this easier.