This should help you understand this issue. It really is pretty simple.
1. Jesus also didn’t say a word about pedophilia, bestiality, or rape. You going to argue those things are ok also? The fact he was silent on this issue is pretty weak.
2. You can’t have it both ways. People on this board always want to reject the Bible as God’s infallible word. Now because you don’t see it mentioned by Jesus you want to use the Bible. If that is the case you need to read what Paul had to say about homosexuality.
3. Why would Jesus need to talk about an issue everyone agreed on? A great portion of Jesus’ ministry related to Israel and those familiar with the Law of Moses. They were living in an age under the Mosaic Covenant, which condemned this act (Lev. 18:22; 20:13).
4. When Jesus did speak about marriage, He affirmed it as an institution between a male and a female. In Matthew 19, the Pharisees asked Him what He thought about divorce, hoping to trap Him into disagreeing with Moses and therefore finding reason for condemning Him. Now, in Jesus’ response about why divorce is a bad thing and a result of the hardness of human hearts, Jesus says, “Have you not read that He who created them from the beginning made them male and female, and said, ‘For this reason a man shall leave his father and mother and be joined to his wife, and the two shall become one flesh’? So they are no longer two, but one flesh. What therefore God has joined together, let no man separate.”
5. All of Scripture is the Word of Jesus, both Old and New Testament. So all of the talk about Jesus not saying anything is simply uneducated talk.