I wouldn't worry about it, as long as it doesn't interfere with your everyday life or end up as PMO.
But I think you could stand to live with the real-life little sister that most folks have. That is, the average little sister that is generally irresponsible, unkempt, imposing, dishonest and not that very good-looking. You know, something just to ground you from those fantasies you've created for yourself over the times by watching those a-nee-mays.
It might just change your perception and in turn your fantasies of them. Just my 2ยข.