Is it normal to have sexual fantasies about your father in law?

I am 21 years old. I am having sexual fantasies about my father in law. I am unhappy with my fiancé. He doesn't look at me like he used to and he cheats on me. Anyways, it all started a couple months after I started dating my fiancé we were all having a good time and his father was drunk me him and his father were sitting in the back of the car I was in the middle and he started rubbing my legs I thought it was so inappropriate because he's my finances father. He did that more and more when he drank then he stopped so I thought nothing of it. Then, recently he started again but not only when he drinks. Every night me his wife and him watch a movie and his wife always falls asleep so when she is sleeping he will do sexual signals toward me and winks at me. I think he is really hot. I usually don't look at older men like I look at him. I dream about him and I always think about doing it with him. What should I do?