I am thinking about having sexual relations with my sister.
Why do you want to have relations with her?
I can't control my feelings for her, and we love each other.
It's not a good thing that you're looking for an intimate relationship with your sister. You need to break off this line of thinking right now and find another woman.
It's my life. I love her and we will do what we please.
Familial sexual relations are looked down upon in society as they are illegitimate, so your wanting your sister will not come across well. There are plenty of women in the world that are not related to you. Go out and get one of them instead.