Well, my siblings and I kind of all have a particular look about us that you can tell makes us related. You would think that your parents (assuming you would tell them you were dating a girl you were going to have sex, telling them about the girl, not the sex of course) would hear her name and be like OH! thats your long lost adopted sister and because we live in a time of free-sex we told you so you wouldn't make a huge mistake and have gross hillbilly sex with your sister. However, that's not the point of a hypothetical, so...I guess after finding out, that is if I'm still the same person I am today. It would be really hard and I'd probably wish that I'd get struck by a lightning bolt or swallowed up by an earthquake. I'd ask her if she was going to keep the child and if so I'd tell her to put it up for adoption. Then change my name, and move the hell away/possibly join the military to get far away as possible, forever. At least that's my hypothetical solution, I wouldn't really know unless it happened.