At the beginning of the film, Kabir (Abhay Deol) proposes to Natasha (Kalki Koechlin). Their families meet at the engagement party. At the party, Natasha learns that Kabir is planning a three-week bachelor road trip to Spain with his school friends Imraan (Farhan Akhtar) and Arjun (Hrithik Roshan). Kabir explains that the three have a long-standing pact, and that during the road trip, each of them will have to pick an adventure sport, which all three will try together. Initially, Arjun is reluctant to take part in the trip due to his workaholism and obsession with money. It is later revealed that Arjun's ex-girlfriend left him due to this reason. Imraan has an additional personal agenda on the tripto find his biological father Salman Habib (Naseeruddin Shah), an artist in Spain.The trio set off to Spain, where they plan to visit Costa Brava, Seville, and Pamplona. On the way to Costa Brava, Imraan and Kabir find it annoying that Arjun works even during the trip. Imran casually throws Arjun's phone out of their car while he was in the middle of an important call. This leads to a misunderstanding, which ends up in a violent argument. Arjun, in a fit of rage, accuses Imraan of having an affair, four years back, with Arjun's previous girlfriend (a topic which was very sensitive both to Arjun and Imraan). After getting consoled by Kabir and reaching their destination, they meet an Indian American named Laila (Katrina Kaif) in a beach. Imraan flirts with her and makes Arjun jealous. Kabir reveals that he has chosen deep sea diving as their first sport, and they later find that Laila is their diving instructor. Arjun, who cannot swim and is aquaphobic, receives assistance from Laila. She helps him overcome his fears and finish the sport successfully. Upon a request by Laila, they attend the La Tomatina festival held in Buñol with her and meet Nuria (Ariadna Cabrol). Meanwhile, Natasha becomes suspicious of Kabir's involvement with Laila and crashes his bachelor party trip, much to Kabir's discomfort in front of his friends. Imraan spends time with Nuria, and Arjun with Laila. After the boys leave, Laila realizes she has fallen in love with Arjun and chases them on a bike, not wanting to regret their partition if they don't meet in future. She and Arjun express their feelings for each other with a passionate kiss.On the way to Seville, Kabir drops Natasha at the airport, while Arjun and Imraan notices that something is wrong between her and Kabir. The trio visit Seville for sky diving, as per Arjun's choice. During the task, Imraan is forced to confront his acrophobia and hesitates to take part. However, they complete it without any obstacles. After skydiving, the three men go to a bar and get into a fight with a stranger on whom they had tried to pull a prank. They are jailed after the fight. Salman, Imraan's father, bails them out and takes them to his home. While speaking to Imraan, Salman reveals that he never wanted the responsibility of a married life with kids, while Imraan's mother did, which is why he never contacted Imraan. Imraan, heartbroken, realises how it would have felt when he had hurt Arjun four years back. He earnestly apologises to Arjun, and he readily forgives Imraan.The trio leave for the bull run in Pamplona, which was Imraan's choice. When confronted by his friends, Kabir confesses to Arjun and Imraan that he is still not ready for a marriage, but could not tell this to Natasha as he did not want to hurt her. On the morning of the Bull-run, Imraan suggests they make a pact to make a promise if they survive the event. Imraan vows to publish his poetry (he was secretly a poet), Arjun vows to go to Morocco with Laila to spend the rest of his life with her, and Kabir promises to tell Natasha that he is not ready to marry her. As they complete the event, the friends gain a renewed sense of their relationships with each other, with others they know, and with themselves.As the credits roll, Imraan, Kabir, Nuria and Natasha are shown attending the wedding of Arjun and Laila in Morocco. Kabir and Natasha did not marry, but remain friends.
Output: Question: Why did Arjun's ex-girlfriend leave him?, Answer: Workaholism and his obsession with money.