One popular one is 'Twilight' by Stephenie Meyer. It features a love triangle between Bella, Edward, and Jacob. Bella is in love with the vampire Edward, but also has a deep connection with the werewolf Jacob.
The 'The Selection' series by Kiera Cass. In this series, America Singer is part of a competition to win the heart of the prince, Maxon. However, she also has feelings for Aspen, her childhood sweetheart, creating a love triangle that drives much of the story's drama.
Another is 'The Vampire Diaries' book series by L. J. Smith. Elena Gilbert finds herself in a love triangle with the vampire Stefan and his brother Damon. Her relationships with both brothers are complex and full of passion, mystery and danger, which keeps readers on the edge of their seats.
The 'The Hunger Games' series also has elements of a love triangle. Katniss is involved with Peeta and Gale. Her relationship with both of them is complicated by the harsh reality of the Hunger Games and the fight for survival, which makes their triangular relationship an interesting aspect of the story.
One popular one is 'Pride and Prejudice' by Jane Austen. It has a sort of love triangle between Elizabeth, Mr. Darcy, and Mr. Wickham. Elizabeth is initially attracted to Wickham, but as the story unfolds, she realizes her true feelings for Darcy.
One popular one is 'Gone with the Wind'. Scarlett loves Ashley, but Ashley is engaged to Melanie, and Rhett Butler also loves Scarlett, creating a complex love triangle set against the backdrop of the American Civil War.
Another example is 'Pride and Prejudice' in a way. Elizabeth Bennett has a complex relationship with Mr. Darcy, but there is also Mr. Wickham in the picture at some points, creating a sort of love triangle dynamic in the context of the story.
Often, the protagonist chooses one of the love interests. For example, in 'Twilight', Bella chooses Edward. This is a common ending as it resolves the central conflict of the love triangle.
Another example is 'Pride and Prejudice' to some extent. Elizabeth Bennet has a complex relationship with Mr. Darcy, but there is also Mr. Wickham in the picture for a while, creating a sort of triangular dynamic in the romantic relationships.
The Twilight series also features a love triangle. Bella is in love with Edward, a vampire, but Jacob, a werewolf, also has strong feelings for her. This love triangle creates a lot of tension and drama throughout the series as Bella has to choose between two very different beings, each with their own allure and drawbacks.
One popular billionaire love triangle novel is 'Fifty Shades' series. It involves a complex relationship between the main characters which has elements of a love triangle. Another one could be 'The Hating Game' which has a bit of a love triangle dynamic in a corporate world involving wealthy characters.
The 'The Hunger Games' series also has elements of a love triangle. Katniss is caught between Peeta and Gale. Peeta is her fellow tribute in the Games, and Gale is her friend from home. Their relationships are complicated by the dangerous and political situation in Panem.
A very popular one is 'Outlander' by Diana Gabaldon. Claire is married to Frank in the 20th century, but then travels back in time and falls in love with Jamie. The love triangle between Claire, Frank, and Jamie spans different time periods and cultures, making it a truly engaging read.