Jesus on sex

Religious Tolerance notes that Jesus only mentions sex a few times.

Summarizing Jesus' statements involving human sexuality:
Divorce: He may or many not have believed that sexual misconduct was a sufficiently serious ground to justify a divorce.

Lust: If Matthew 5:27-28 does refer to lust directed at another man's wife, then a clearer translation into English of Matthew 5:27-28 might be:

"Ye have heard that it was said by them of old time, Thou shalt not commit adultery: But I say unto you, that whosoever looketh on [another man's] wife with an obsessive consuming lust hath committed adultery with her already in his heart."

That is, normal feelings of attraction are not sinful.
The Samaritan woman: The quotation from John 4 may or may not criticize the woman's sexual behavior and marital history.
The adulteress: The quotation from John 8 appears to be a forgery by an unknown author, which is not part of the original gospel of John. Its authority is questionable.

So, a case can be made that Jesus was totally silent on matters relating to sexual behavior except for the special case involving obsessive feelings of lust towards a married person other than one's spouse.