It is vital to keep in mind that, when Oscar Wilde wrote The Importance of Being Earnest, he was specific in its subtitle: "a trivial comedy for serious people."
This being said, Wilde never intended to present the theme of love under a serious light. In fact, he intended to mock it as a sentiment that is as fickle as a whim. He also wanted to expose the unrealistic expectations placed upon love as a precursor of marriage, thus satirizing and criticizing the Victorian institution of marriage as a whole. Therefore, the elements that help develop the theme of love in the play are quite weak, yet, they do exist, to be fair.
The first indication of courtship and love comes in Act I where Jack declares his love for Gwendolen to her cousin, Algernon, who is Jack's best friend. In this declaration we see the traditional elements of courtship illustrated by Jack's idealization of Gwendolen as the perfect woman, and by stating his clear intentions of marrying her. Immediately, however, Wilde blocks this seemingly romantic state with Algernon's remarks of how Lady Bracknell could never consent, and by setting the problem of the play,which is the true identity of Jack Worthing.
However, the storyline between Jack and Gwendolen continues until the end of the play. Gwendolen plans an elopement (as the audience can discern, from her rebellious visit to Jack in the countryside), and is met by a potential rival in Cecily, who is just Jack's ward. The subsequent interview between the two ladies, and the eventual showdown where each claims the elusive "Ernest" as their own, develops the theme of love in that both women have set their hopes quite high in their engagements and in the way in which they plan to take care of their "dear Ernests".
The clarification that ensues shows the two ladies that they have both been duped. However, far from this becoming a dramatic moment, Wilde makes it funny by having the women run inside the house expecting the men to chase them and ask for forgiveness. Contrary to the expectation, the men do not chase the women but, instead, eat the ladies' muffins and cake and sit down to tea, basically.
On a separate note, Cecily also adds to the theme of love by becoming Algernon's own love interest. Their particular storyline is infused with comedy and silliness considering how Cecily treats Algernon as a child, and how Algernon's love for Cecily keeps being interrupted by his incessant hunger (Wilde's allegory to the lack of fulfilment that women cause in men). Yet, their storyline it does sustain elements that develop the theme of love, such as chivalry (Algernon's refusal to leave Cecily's side despite Jack's threats), and his insistence in that Cecily is also the perfect woman.
The play ends with everybody finding their "true loves", despite of their convoluted and superficial courtships: Prism and Chausible, Cecily and Algy, and Gwendolen and Jack all claim each other under Jack's sarcastic remark about the true importance of being "earnest", which truly shows Wilde's opinion about the flakiness of love. However, Wilde does use chivalry, intense emotion, the elements of courtship, idealization, and the hopes for a "good match" as very realistic and basic elements to develop the theme of love in the play. He does this fantastically, as this is his most timeless play of all.