P43: Hate is increased by being returned, but can be destroyed by Love.

Dem.: He who imagines one he hates to be affected with Hate toward him will feel a new Hate (by P40), while the first (by hypothesis) continues. If, on the other hand, he imagines that the one he hates is affected with love toward him, then insofar as he imagines this, he regards himself with Joy (by P30) and will strive to please the one he hates (by P29), i.e. (by P41), he strives not to hate him and not to affect him with Sadness. This striving (by P37) will be greater or lesser in proportion to the affect from which it arises. So if it is greater than that which arises from hate, and by which he strives to affect the thing he hates with Sadness (by P26), then it will prevail over it and efface the Hate from his mind, q.e.d.