ove is a passion that is hurtful to the lover?

(6) Whether love is cause of all that the lover does?
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FIRST ARTICLE [I-II, Q. 28, Art. 1]

Whether Union Is an Effect of Love?

Objection 1: It would seem that union is not an effect of love. For
absence is incompatible with union. But love is compatible with
absence; for the Apostle says (Gal. 4:18): "Be zealous for that which
is good in a good thing always" (speaking of himself, according to a
gloss), "and not only when I am present with you." Therefore union is
not an effect of love.

Obj. 2: Further, every union is either according to essence, thus
form is united to matter, accident to subject, and a part to the
whole, or to another part in order to make up the whole: or according
to likeness, in genus, species, or accident. But love does not cause
union of essence; else love could not be between things essentially
distinct. On the other hand, love does not cause union of likeness,
but rather is caused by it, as stated above (Q. 27, A. 3). Therefore
union is not an effect of love.

Obj. 3: Further, the sense in act is the sensible in act, and the
intellect in act is the thing actually understood. But the lover in
act is not the beloved in act. Therefore union is the effect of
knowledge rather than of love.

_On the contrary,_ Dionysius says (Div. Nom. iv) that every love is a
"unitive love."

_I answer that,_ The union of lover and beloved is twofold. The first
is real union; for instance, when the beloved is present with the
lover. The second is union of affection: and this union must be
considered in relation to the preceding apprehension; since movement
of the appetite follows apprehension. Now love being twofold, viz.
love of concupiscence and love of friendship; each of these arises
from a kind of apprehension of the oneness of the thing loved with
the lover. For when we love a thing, by desiring it, we apprehend it
as belonging to our well-being. In like manner when a man loves
another with the love of friendship, he wills good to him, just as he
wills good to himself: wherefore he apprehends him as his other self,
in so far, to wit, as he wills good to him as to himself. Hence a
friend is called a man's "other self" (Ethic. ix, 4), and Augustine
says (Confess. iv, 6), "Well did one say to his friend: Thou half of
my soul."

The first of these unions is caused _effectively_ by love; because
love moves man to desire and seek