Whenever mortals fall in love,
if they should happen to meet with fine lovers,
there is no greater joy than this.

[ὅσοι γὰρ εἰς ἔρωτα πίπτουσιν βροτῶν,.
ἐσθλῶν ὅταν τύχωσι τῶν ἐρωμένων,.
οὐκ ἔσθ’ ὁποίας λείπεται τόδ’ ἡδονῆς.]

Euripides (485?-406? BC) Greek tragic dramatist

Andromeda [Ανδρομέδα], frag. 138 (TGF) (412 BC) [tr. Wright (2017)]
    (Source)

One of the first recorded uses of the phrase "fall in love [εἰς ἔρωτα πίπτειν]."

Nauck frag. 138, Barnes frag. 24, Musgrave frag. 12. (Source (Greek)). Alternate translations:

They who by love are caught, and fix their love
On virtuous objects; to complete their bliss,
Can need no new accession of delight.
[tr. Wodhall (1809)]

When it befalls poor mortal men to love,
Should they find worthy objects for their loving,
There is no fuller joy on earth to long for.
[Source]