That would depend on what you mean. If you mean that a dementia patient is confusing the person he or she is talking with as his or her sex partner of many years, then yes, this happens. This person may have forgotten that his wife is elderly, or even who she is, and start to make passes at his daughter or daugher-in-law, thinking it's okay. He may think he's in high school and that some young girl is pretty and that he's a "cute guy." It only means that this person doesn't understand the true realtionship or what it means.

If the person doesn't have  diagnosed dementia, you may be dealing with something else. A doctor should be consulted in either case.

Carol