Love is nothing else but pleasure accompanied by the idea of an external cause: Hate is nothing else but pain accompanied by the idea of an external cause.

We further see, that he who loves necessarily endeavours to have, and to keep present to him, the object of his love; while he who hates endeavours to remove and destroy the object of his hatred.
But I will treat of these matters at more length hereafter.
PROP.XIV.

If the mind has once been affected by two emotions at the same time, it will, whenever it is afterwards affected by one of these two, be also affected by the other.
Proof .-- If the human body has once been affected by two bodies at once, whenever afterwards the mind conceives one of them, it will straightway remember the other also (II.

xviii.).

But the mind's conceptions indicate rather the emotions of our body than the nature of external bodies (II.xvi.Coroll.