Yet loneliness shall weary thee, and still
Love torture thee with longings nought can fill.
Absence makes passion’s tide have double sway,
Possession cloys the love of every day.

[Nulla tamen lecto recipit se sola libenter:
Est quiddam, quod vos quaerere cogat Amor.
Semper in absentes felicior aestus amantes:
Elevat assiduos copia longa viros.]

Propertius (50-16 BC) Roman elegiac poet [Sextus Propertius]

Elegies, Book 2, No. 33C, “To Cynthia,” ll. 41-44 [tr. Moore (1870); 3.25]
    (Source)

This quote (the third line) appears to be the origin of the English proverb, "Absence makes the heart grow fonder." The first use of those exact words appear to be from a song by T. H. Bayly, "Isle of Beauty, Fare Thee Well" (1826?). For more discussion of the origin (and variants) of that phrase see etymology - Who is the author of "Absence makes the heart grow fonder"? - English Language & Usage Stack Exchange.

Not surprisingly, the idea of absence increasing (or decreasing) ardor is a a frequently discussed theme. See this English Proverb; Cervantes (1605); Rabutin (1660); La Rochefoucauld (1678); Johnson (1758); Mirabeau (1770); Ouida (1878); Antrim (1905); Shaw (1931); Bowen (1938); Stark (1953).

Propertius' elegies, as handed down, are something of a mess, and the assignment to them in particular books has been of sharp debate. This passage is currently considered a fragment, connected to 2.33 (and called 2.33A, or 2.33B, or 2.33C by different translators); similarly, the line numbering in sometimes carried across the entire 2.33, other times broken between the fragments. This fragmentary nature is also why the two couplets here appear in different order between different translations.

Nineteenth Century sources, based on the manuscript traditions of the time, assign this as 3.25.

(Source (Latin)). Other translations:

Yet loath to bed her way lone maiden wends,
Love keeps her brooding o'er forbidden joys;
More deeply yearns the heart for absent friends:
Even of the leal [loyal] the long possession cloys.
[tr. Cranstoun (1875); 3.25]

But no one retires with good will to her solitary couch. There is something that Love forces you to miss. There is always a more favourable disposition towards absent lovers; long possession lowers the value even of the devoted.
[tr. Gantillon (1880); 3.25]

No woman takes herself cheerfully to bed alone though: there is something which Love makes you fain to look for.
Desire always burns kindlier toward absent lovers: long plenty of opportunity makes cheap the never-failing suitor.
[tr. Phillimore (1906); 2.33]

Yet no woman ever betakes her willingly to a lonely bed; there is a somewhat that Love compels all to seek. Woman's heart is kinder always towards absent lovers; long possession takes from the worth of the persistent wooer.
[tr. Butler (1912); 2.33]

Woman's heart is ever fonder towards an absent lover: long possession lessens the appeal of the persistent wooer. Yet no woman willingly retires to bed alone: there is something which Love compels you all to seek.
[tr. Goold (Loeb) (1990); frag. 2.33C]

No girl ever willingly goes to bed alone: something there is desire leads us all to search for. Passion is often greater in absent lovers: endless presence reduces the man who’s always around.
[tr. Kline (2008); 2.33A]

Passion helps the absent lover: long persistence
elevates the assiduous man.
No man gladly goes to bed alone, for Amor
gives us something all must seek.
[tr. Holcombe (2009); frag. 2.33C]