Not a bad spell at all; i bet it could work under the right circumstances. Congrats, if you in fact wrote it. Did you have success with the break-up work?
All along i was expecting the knots to be untied, as in dissolving the bond between the couple, but you went about it in a different way - knots to hold in the anger, if i am correct? It's an interesting approach.
If you want some unsolicited feedback, i'd add more about the disposal, what to do when the active part of the spell is done, how to dispose of the remnants, and what to do with the string of knots.