"Cupboard love" is an English expression referring to affection that is given purely to gain a reward.
The phrase is most often applied to human activity, for example, when a child will say "I love you so much" before or after requesting a treat, for example, an ice cream. Cupboard love is a milder version of conditional love, where love is given solely in response to certain behaviour. The earliest known usage of the term, possibly the first usage, is in the 1756 volume of British court records, The Proceedings at the New Bayley. “Now, there is a Kind of Love in the Old Stile, termed Cupboard Love; and it often happens, that what People judge to be an Intrigue with a young Woman, turns out, on a nearer View, to be only an Intrigue with a Leg of Mutton and Turnips. This Kind of Love is frequently seen among certain Gentlemen at Counry Quarters, the Curates in City Parishes, Attornies Clerks, and young Barrister, and may, doubtless, descend to all Persons who have larger Stomachs than Purses. So, Gentlemen, go out.”
Example in Literature: From page 47 of the children's book Miss Hickory by Carolyn Sherwin Bailey, copyright 1946: "Cow had been gone from the barn all day, and Mr. T. Willard-Brown [a tomcat] was anxious about her. Not on Cow's account. Oh, no! He had only cupboard love for Cow and had missed his daily saucer of warm milk."