Really weird story but it can be true.
My brother thought this girl was hot as fuck then her mom got married to my uncle, she became my cousin in-law.
Just because she is my cousin in-law, my brother says he can't check her out no more..
Kind of weird but things like this happen.
As for your story, I believe its true but you aren't explaining the backround of your life too good because if you lived with your sister for your entire life, you shouldn't think shes a hottie at all.
She would just be another pain in the ass.
But good job getting over her and good luck with everything bro
something similar happend to me w. this cousin thing and it fucking sucks might i say...