eerrrgghhh what.
I did once read a really sad story about a half-brother and sister, who had the same biological father, and had met and fallen in love BEFORE they found out they were related. I think they stayed together and moved abroad where no one would know them. A very complicated situation, then... I mean, if I suddenly found out that by some bizarre coincidence, my dad had gotten my mother-in-law pregnant 30 years ago and my wife was actually my half sister... I wouldn't suddenly stop loving her like a partner
.