I feel like a bad mother because I fantasize about my son and daughter

Hello, my name is Polina. I'm pretty embarrassed to be on this forum. Maybe I should tell you a little bit about myself. I'm a mother of two ****. I love them very much. I have a daughter and a son, my daughter is a little younger, she is 18 years old. My son is 21, he is a very good boy. I have a wonderful relationship with them. There is only one unpleasant detail, my husband divorced me two years ago and got married right away. It was very painful for me because I was sure that he loved me. I still don't know why he left me. I also realized that he had never given me enough pleasure in bed, but I had been shy and modest all my life, so I never demanded more. I'm embarrassed to say this, but while I was married, I didn't masturbate at all, which I regret now. After the divorce, I began masturbating a lot, but I've never had toys and still don't have them. Strangely, I always fantasize about my ********. At first, only about my son, and recently I began to fantasize about my daughter, despite the fact I have never been attracted to women. I feel dirty because of such thoughts, but I can't do anything about it. English is not my native language, but I tried very hard to type correctly. I spend a lot of time with my daughter since she now lives with me, but my son lives at home some days, and some days in another place. When I look at them, I always have vulgar thoughts in my head. It was very embarrassing for me to type this text because I had never discussed such topics. But I'm trying to figure out what to do next