They never tell you when you're a kid that much of what you consider family, May not be family at all. Very few of the people your close to will even be related to you. I got a response to one of my posts about death and the person was very distraught at the death of a coworker. I have coworkers that are as close to me as any family I have. You become attached to people as you move through life. I mean even looking at my family now. I am not related to any of the people in my house. My wife I am related to through marriage and my child through adoption.
I often think way too much emphasis is put on blood relation. At least for me, blood relation doesn't entitle you to anymore than anyone else. I'm close to my mom because she raised me and we're fairly similar. My sister Brandi I'm close to as well, but I think even if we weren't related we'd be good friends.