Why are Brother and Sister relationships so intense and sometimes end up in a sexual relationship?

My sis and I grew up loving each other deeply.


We have been best friends forever.


We have enjoyed some really intense experiences from early ages to age 14 when we finally realized that we had to stop being so close. I am just curious how many have been in this situation ?Why are Brother and Sister relationships so intense and sometimes end up in a sexual relationship?
well did you or didn't you???????????????????