This is how I explain it to people.

Some people forget to eat lunch. That is baffling to me. Like, I literally schedule my entire day around when/what I'm going to eat. I love trying new food and new places. But to other people they just don't care much about eating. It's not a big part of their life. That's how I am with relationships.

Another example is exercise. Some people just don't care about working out. I think it's very important and try to make myself better everyday through exercise. I could not imagine a life without sports. For some people they are perfectly happy without sports. That is how I am without relationships.

Sleep is also a great example. To me, sleep is pretty much the greatest thing ever invented. Other people don't, and they are crazy people.

When someone you know questions you on it, relate the fact that you just don't care that much about relationships to something in their life that they do or don't care that much about. Usually when I explain that, people get it.