[27m] My sister[23f] is going out with a man [32m] who has an autistic son. How do I see off my sister as she does not want to go out with that man?

My [23f] sister has been going out with a [32m] man. He had gotten married 4 years ago but got divorced 2 years ago after his child was born. I do not know the reason for their separation. Today my sister has told me that the man has an autistic child. I do not want my sister to go out with a man who has an autistic child. I do not want my sister to see off as she has been interested to go out with that man. How do I see off my sister as she does not want to live happily?<br><br>Edit : She has not gone out with that man until today. She has been talking with that man for the last 2 weeks. She has got to know that the man has an autistic child today.