"But he's like a brother
I can tell you exactly what people who claim this are doing. I've been doing it for two years now.
Actually, the way I usually say it is (imagine drunken slurring), "For the billionth time, NO! I could NEVER sleep with him. That would be sooooo incestuous! Eeee-EEE-YEW!" The reason I do this is not because I'm attracted to him. It goes much deeper. -sigh-
He and I are madly in love in a strangely wonderful psychic/emotional/intellectual way. It doesn't hurt that he is the most physically attractive man I've ever met. But his looks disappeared to me a long time ago. When I look at him now, I barely notice those gorgeous cheekbones. I'm too busy loving what's behind his eyes.
We both use the sibling excuse. Sometimes we sit with our mutual friends and elaborate on it together:
"Gross! He's like a brother!"
"Yeah! I've known Jen too long to fuck her!"
"Besides, he's too scrawny!"
"And her boobs are too big!"
"And... (Dude, we need to shut up now)"
The weirdest part is that we both realize why we're putting off the inevitable. Once we get together, we're stuck. Forever. Not that it will be bad. But there's no way I'm gonna spawn yet. And besides... he's like a brother!