Q.E.D.
Corollary .-- A lover will, therefore, feel pain if one of the aforesaid attendant circumstances be missing.
Proof .-- For, in so far as he finds some circumstance to be missing, he conceives something which excludes its existence.

As he is assumed to be desirous for love's sake of that thing or circumstance (by the last Prop.), he will, in so far as he conceives it to be missing, feel pain (III.

xix.).

Q.E.D.
Note .-- This pain, in so far as it has reference to the absence of the object of love, is called Regret.
PROP.XXXVII.

Desire arising through pain or pleasure, hatred or love, is greater in proportion as the emotion is greater.
Proof .-- Pain diminishes or constrains a man's power of activity (III.xi.