I've heard of Duality. I'm actually INFj in Socionics, so ESTjs are my dual relation. That's why my friend gets along with me. We can hang out for six hours in a day. We can also text each other for hours. He's ESTJ and ESTj. But I think we do need occasional breaks.
But I am also 96% likely to be INFp, according to one Socionics test, so that could explain the duality between him and me.