>>321996
>she is a sikh.
Your relationship is fucked, dude. She has probably not told anyone in her family that she is banging a white man.
>what is with you guys and not wanting your people to marry outside race/caste/religion?
Castes
Every society eventually develops hypergamy. There were four castes which represented the jobs assigned to them in the society. And everyone wanted to marry up.
The Brahmins were on the top. So, they had no interest in sending their daughters into lower caste houses, obviously. They were not interested in taking brides from lower castes and diluting their bloodlines. So, they created dogmas that people should marry within their castes. Some Brahmin subcastes in South India, actually marry their cousins to keep their bloodlines pure.
Most of these dogmas were passed down generations through oral traditions rather than texts. Some modern internet Hindu apologists actually believe that there is no caste system in Hindu texts. But, there are actually several references to castes. As castes divided into subcastes, the dogma continued, resulting in the current mess.
Sikhism and gotras
People in the Haryana and Punjab (Sikhs come from Punjab) region used to live in tiny farming communities. There was always the chance of inbreeding. So, they introduced the concept of gotra, that is don't marry anyone who may have shared a patrilinear ancestor with you. But, the population has grown so much since then, that the chances of inbreeding is almost zero, but the dogma persists.
(In South India, it is the opposite. The Brahmins try to marry within their gotram, as it is called there.)
Then hypergamy came into play. People wanted to send their daughters into richer gotras, because you can't marry within your gotra and it is dishonourable to marry down. This raised the price of dowry. Some men began killing their newborn girls. (https://en.wikipedia.org/wiki/Kuri-mar) Now, they check by ultrasound and abort female fetuses.
Sikhism essentially splintered from Hinduism, and rose as a religion of war in response to the Muslim invaders. Their founder was both their guru and general. They have a strong sense of honour. Haryana and Punjab report the highest number of honour killings in India. They also have the lowest female to male birth ratios.
Foreigners
The Europeans which the ancient Hindus encountered were mostly the Greek invaders. They were called the Yavana or Yona. But, it is still disputed where they fit in the pyramid.
Trying to fit a white man into this mess is sure complicated for the conservatives. So, they simply forbid their children from dating white people.
Modern scenario
Modern education and industrialization was the great leveler. Now, even a low caste can get an education and get a good job. But, people still cling to dogmas. Hypergamy exists but people want the best groom within their caste for their daughter. This causes an artificial scarcity, raising the dowry prices. Sometimes when a groom or his family feels that the dowry is insufficient, they may torture or kill the bride. (https://en.wikipedia.org/wiki/Dowry_death)
Furthermore, the government introduced affirmative action policies for lower castes. They have certain percentage of university seats and public sector jobs reserved for them. These are valuable due to the highly competitive education and job market. So, now it is in the lower castes' interest to not marry into higher castes, because they will lose these benefits then. Thus, the caste system persists due to dogma and government policies.
People who marry across castes lines are usually liberals. Conservatives rarely marry across caste lines. When they do, it is usually because the groom is very valuable, like a millionaire or something.