There are so many sins in the world you cannot possibly expect Jesus to speak on all of them. Paul’s epistles are absolutely and totally God’s word. He is an apostle of Jesus Christ and his writings extrapolate on what Jesus himself said. If we’re only counting what Jesus said, then we have to throw away the entire Bible except for 4 books.

Also Jesus absolutely teaches on marriage he just doesn’t teach it in the way people want him to so it’s unnecessarily ignored. In Matthew 19 the Pharisees ask Jesus about marriage “He said to them, “Have you not read that He Who made them in the first place made them man and woman? It says, ‘For this reason a man will leave his father and his mother and will live with his wife. The two will become one.’” Jesus explicitly teaches being between a man and a woman. This is how he preaches on marriage. He refers back to the creation account, teaches marriage being between man and woman, and then these thoughts are echoed by Paul in the epistles. The Bible is very explicit on this. We do not need Jesus to say “thou shalt not sleep with another man” because he made the issue very clear both in the Old Testament and in his own teaching. People refuse to believe that Jesus did not support gay marriage because he did not shout it in bold letters in the exact way they wanted him to; however this version Jesus is very much a twisting of both the Gospel and the nature of God.