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.