Father has dementia he thinks I am his wife and should be intimate with him.

I'm so sorry. If it's any comfort, this is very common. As you say, he can't tell the difference between you and his late wife. In his mind he is likely quite young, and you may look somewhat like your mother at a younger age, so it's even more confusing for him than for some men.
Many men with AD get sexually aggressive with female caregivers. But, as you say, it's feels even creepier when it's your dad.
Please try to understand that he can't help it. You may want to talk to his doctor. Occasionally, they give medication to handle this, but there are side effects. At least check, though. There may be something the doctor can do to make your life a bit easier. Good luck,
Carol

My husband with dementia did the same thing to our daughter. She was so creeped out that she left. She is just 23. It happened while I was at work. He does know the difference when our daughter and I are together. Our son lives with us to help me care for him when I am gone. My husband (his dad) accuses us of having a inappropriate sexual affair. This is so creepy beyond belief. Its so sad too. My husband will and has told this to his family members and hospital staff. He is focused on his sexual desires and will not let me sleep. Its all he talks about all day to anyone. He is just that sick. I am trying to keep him home but its getting harder. I would not feel safe living alone with him and am so glad my son is here to witness all of his behaviors.