I can't stop fantasizing about having a sister wife.
I am very concerned, why do you fantasize having a sister wife?
I fantasize about being the servant of a hot wife, serving her for the rest of my life.
While no one is harmed with fantasies, you could end up normalizing the behavior and seeing nothing wrong with having your sister as a wife and that will be a harmful thing to do if you act on it later. I do hope you focus on your own relationship and not have any more fantasies about your sister as it is very illegal if you act on it.
I think I'm going to go through with it.
I strongly suggest that you do not as your sister may be really hurt in the process and report you to the police. I suggest you focus on getting a partner that is not your relative so that you can focus your energy making someone happy and in turn will make you happy as well. It's safer and healthier, with no legal problems.