This is an interesting question because it was in the 1700s (the 18th century) that English ideas about love and marriage reached a high state of flux. This drive for change was propelled by writers like Daniel Defoe and Samuel Richardson and the protests of writers like Mary Astell. According to Wendy Moore in "Love and Marriage in 18th-Century Britain," published by The Johns Hopkins University Press, English marriage, indeed European marriage in general, was arranged with respect of wealth and power, with the bride and groom having no say in the bargain at all. Often, marriage arrangements were made at birth. This is referred to in Jane Auten's Pride and Prejudice when Lady Catherine de Bourgh tells Elizabeth that Darcy and Miss de Bourgh had been betrothed since birth. [Interestingly, Austen wrote this in the 18th century (1796-97) though it was published in the 19th (1813).]
It was during the 1700s (18th century) that this wealth and power arrangement of marriage was rebelled against. It was partly the result of the new milieu of social Romanticism in which young lovers would rather end their lives than participate in a loveless arranged marriage and partly because of the Age of Enlightenment brought about by thinkers like Bacon, Hobbes, Locke and Hume. Rousseau (1712-1778) was a product of the Enlightenment.
Thus, English literature of the 18th century expresses the theme of love in keeping with this new spirit of rebellion against loveless, power- and wealth-motivated marriage. Examples pointed out by Moore are Defoe's Roxanna and Richardson's Pamela. Richardson is noted as an influence on Fanny Burney's Evelina. A good example of this trend is The Ruined Cottage by Wordsworth. This poem tells that (1) the lower, laboring classes were relatively free to choose marriage for love (or for the legitimacy of an upcoming birth) and that (2) death is preferred to the loss of love, to a life without love. Another good example is the poetry of Keats, such as "Bright Star," in which love is idealized and its absence sorely bemoaned. Additionally, Keats revives the tradition of Greek and Roman classical allusion to convey these concepts of love--especially the concept of the immortalization of love--in his poetry, such as in "Ode on a Grecian Urn."
In short, the theme of love in the 18th century emphasizes mutual love, mutual esteem and freedom to choose. This informed and reflects the English 1753 Marriage Act that regulates consent without coercion, standardizes the marriage ceremony, and regulates parental involvement in marriage coercion. Additionally, this is reflected in literature like Pride and Prejudice in which Elizabeth makes so bold as to refuse Mr. Collins, even though her sisters' and mother's future security hinges upon her accepting him, and makes equally bold in defying Lady Catherine's demands that she not become engaged to Darcy: power and wealth is bested by individual dignity and love, while young women are protected in their choices.
In the eighteenth century in England, as is most periods of literature, love is a frequently treated theme.
One major genre of the period was Restoration Comedy, a type of comedy of manners that satirizes the self-serving and often manipulative and underhanded approach to love among the upper classes. Examples would be Congreve, The Way of the World and revivals of earlier plays. By mid-century, sentimental drama such as Lilo's London Merchant became popular.
Poetry of the period treats love both satirically, as in Pope's Rape of the Lock, and sentimentally, as in works of Grey, Collins, and later poets.
Novels treat love in a wide variety of contexts, dealing with both the bourgeois and aristocracy.