His parents and her parents have arranged that Robert and Isabelle will marry. When he arrives at her father's castle, he finds Isabelle attractive, but her cousin Matilda is stunning.
William sees Esmeralda in her family's box at a play. Securing an introduction, he calls, meaning that he meets her quiet and plain sister Helen, who is the one who actually makes him welcome; after many calls, he realizes that while he still thinks Esmeralda stunning and vivacious, Helen's quiet virtues and courtesy have grown on him.
Exaggerated: Honest, pretty, good-natured, church girl Alice and stunningly beautiful exotic criminal vampiress Carol both want Bob.
Downplayed: Alice and Carol have mostly similar personalities, but there are a few differences between how the girls behave.
Bob is having an affair with both of them at the same time.
Alice and Carol are different incarnations or aspects of the same person (clones, present/future versions, alternate reality twins).
Bob has to marry either Alice or Carol, but neither of them wants him.
For political reasons, Prince Robert has to marry either the calm and elegant Lady Alisandre, or her vivacious sister Lady Catherina, though they hate him and vice versa; he's torn between Alisandre's patience with his antics and patent disapproval of his life, and Catherina's greater interest in entertainments, and the way she will insist on having some of the fun herself.
Alice and Carol are in love with Bob, but he ends up entering a relationship with Dana.
Alice and Carol both pretend to be in love with Bob for their own reasons, but they aren't. Maybe they're just in it for the competition, or they both actually want Darren but think they can't have him.
None of them have a problem with polygamy.
If homo- or bisexuality is involved, Alice and Carol fall for each other and tell Bob where to go.
Alice and Carol realize separately that Bob can't choose. Alice is so repulsed by his attraction to a dishonest vamp that she dumps him; Carol is shocked that he finds Alice's sweetness and love of home attractive and dumps him before he asks her to marry him.
Alice likes Bob and Carol, Bob likes Alice and Carol, Carol wants the others as Just Friends but is too nice to say anything or enjoys the attention.
Bob eventually chooses Carol. That feeling of unrequited love drives Alice to move to another neighborhood, or even town, simply so she wouldn't have to associate with Bob.
Reconstructed: Alice and Carol are in love with Bob, and the resulting strain this three-way triangle places on them ends up ultimately destroying the relationships between all three. They eventually manage to repair their relationships and come to an accommodation.