In all seriousness, I moved out with my step sister shortly after finishing school and it was actually a really functional relationship, even though was a very dysfunctional human being.

You had the companionship of a close friend, that didn't have the traditional responsibilities of family - our parents only got together about 2 years before we moved out - but because it wasn't romantic we could still pursue a love life independently without the jealousy or desperation you might otherwise have. It also helped that I'm a cis male and she is a lesbian - so we had similar interests in that way.

We lived together for two years and I sort of count it as one of my "serious" relationships - I had 2, 2 year+ relationships before this, and the next one was my wife - who I met at the next share house!