My friend's guardian is now mine (too)
 

It it at all common for guardians and the like to transfer between people who know each other, or for them to be shared?

I'm curious because the guardian of one of my closest friends has recently become mine, apparently. I've known this girl for over a decade now, and in that time plus all the trouble we've gotten into I've become passingly familiar with his presence, but I've never sought out a guardian or guides of my own nor been contacted by any. He just kind of stepped up to the plate this last weekend.

It's not a subject I'm at all familiar with, but I don't think I've heard of this happening before. Mostly, I'm curious why I might be sharing one (not that I'm not used to sharing with my friend already, sigh) instead of winding up with a different one entirely. Isn't that, er, usually how these things go?