It's essential to recognize that fantasizing about a family member, such as your sister-in-law, can be a complicated and sensitive issue. Sharing these thoughts with her would not be appropriate and could potentially lead to significant harm, damage to relationships, and uncomfortable situations for both of you.
Fantasies are a normal part of human sexuality, and many people have fleeting thoughts or imaginations that they don't act on. However, it's crucial to manage these thoughts in a healthy way and not engage in any behaviors that could jeopardize your relationships or cause distress.
If you find that these thoughts are causing you significant distress or sleepless nights, it might be beneficial to discuss these feelings with a mental health professional, such as a therapist or counselor. They can help you explore the underlying emotions and provide guidance on how to cope with these feelings in a healthy and constructive manner.
It's essential to remember the boundaries and respect the relationships within your family. Open communication and seeking appropriate support are vital steps toward managing these emotions and maintaining healthy relationships with your loved ones.