My boyfriend and I are like that. We actually met through Mibba. He said something interesting one night that really spoke to me. "Love is composed of a single soul inhabiting two bodies." I think that explains it quite nicely. I know how you feel exactly. :)
I have that except with my friend who I call twin or my sister. She lives in Mexico and we only been together like 5 times before she moved but seriously we are so0o0o the same it's scary. We even have that mental connection going on.