The irony of love as an illness
Another common irony in romance literature is that love is commonly shown to be a negative feeling, a type of suffering. This story does this by Philetas's treatment of love as a disease with a cure, and the cure is kissing. Cute.
The irony of Chloe's suitors
By abiding his social pressures against fornication, Daphnis leaves Chloe as a virgin, meaning that her life quickly fills up with suitors and pushy men who even try to kidnap her. The irony here is that by allowing Chloe to come to her full adulthood before the two consummate their relationship, he risks losing her.
The irony of Daphnis's abduction
This leads to the next irony, the ironic abduction of the male character. His story seems to be a narrative showing his character's journey to sexual confidence, especially confidence as a man. By his abduction and his near-rape scene, the story is bring attention to Daphnis's relationship to other men, and to himself. This is shown to be a prerequisite to romance, coming to sexual confidence by working through one's relationship to masculinity.
The ironic revelation of the birth parents
Interestingly, it's not the adoptive parents who bring Daphnis and Chloe together, but the original parents. Maybe this is supposed to represent the two of them coming to terms with their difficult abandonment issues, finally finding peace with their real parents.