But siblings share intimacy without sharing a bed. Why can't they?
"Any sort of sexual thing is a natural bonding process," Cameron said. "This need to be together could actually be a fear of being apart again because you haven't grown up together."
Another theory: The social taboo isn't an issue for them, psychotherapist Soll said. "If you don't grow up with your brother or sister," he said, "one doesn't have that in-built taboo that children do have who have grown up together."
The taboo exists for most of us, and incest is illegal in all but a handful of countries because children born of incest often suffer genetic abnormalities. The question of children is not one that Cameron and Heaney face. She was sterilized after suffering severe postnatal depression after the birth of the daughter she had with her husband. Her ex-husband has custody of their child.
Despite all the problems they face, Cameron and Heaney are determined to stay together. "I still feel that I've found my soul mate," Heaney said. "And I'm not letting him go for anything."
One day they hope to move to France, where their love is legal.