Is that something you can ever get over?
Incestuous relationships are probably the most taboo out there without resorting to forcing yourself on someone. Having intercourse with your blood relative is seen as absolutely disgusting, yet it occurs more than you want to realize. For those of us who have crossed that line, this is how it happened and how they dealt with it afterwards.
This particular brand of taboo sex is one of the more popular forms of fantasy. Just check out adult sites to prove it. But what about those who actually did it?