Of course Jesus never talked about incest. Then Christians would have to explain how one man and one woman populated the entire world without resorting to it.
God did. In Leviticus:
“None of you shall approach any one of his close relatives to uncover nakedness. I am the Lord. You shall not uncover the nakedness of your father, which is the nakedness of your mother; she is your mother, you shall not uncover her nakedness. You shall not uncover the nakedness of your father's wife; it is your father's nakedness. You shall not uncover the nakedness of your sister, your father's daughter or your mother's daughter, whether brought up in the family or in another home. You shall not uncover the nakedness of your son's daughter or of your daughter's daughter, for their nakedness is your own nakedness."
Leviticus 18:6-18
And perhaps reading this would help:
Why did God allow incest in the Bible?