After college, there's two main ways to make friends: churches and bars. If you don't like religion or alcohol, you better like being alone. I'm a church person, so I don't know if bars are like this, but our churches have a huge racial segregation problem. Martin Luther King Jr. said "eleven o'clock Sunday morning is the most segregated hour and Sunday school is still the most segregated school of the week." (source)
My church is almost all-white. We have a few Hispanics but we don't have any black members now. We used to but they moved. Since then we haven't had any new black members. Segregation extends to other things too. Most events I go to are all-white or almost all-white. There's no "whites only" sign on the doors but it turns out that way.
Why? There's a big culture difference. Race has little to do with heritage and lots to do with culture. A good example: My musical taste is very white. I like plenty of musicians of other races, but they all have lots of white fans. Different races go to different social events. They're involved in different clubs. Sometimes they have different hobbies.
That's one reason there aren't a lot of interracial relationships. The ones that work best are the ones with less culture gap. Either the partners are interested in each other's culture or one of them is part of the other race's culture. I'm all for interracial marriage, but sometimes I feel bad for kids who are pulled between two cultures and aren't "white" enough or "black" enough. It extends to other races here: a Samoan friend of mine faces the same issue. There's hardly any Samoans in Mississippi.
Beverly Daniel Tatum wrote a book called Why Are All the Black Kids Sitting Together in the Cafeteria? It challenged my thoughts on race more than anything else I've read. Here's a summary of the book. It made me think a lot about race and racial identity. It explains a lot of why society's still so segregated. I don't like segregation but I see why it still exists. I don't know if I agree with everything she says but it's worth a read.
Still, it sucks that I never see most of my black Facebook friends any more. It's not like they're less like me than my white friends. They're part of a different culture.