Jesus never said anything condemning homosexuality, so that must mean it's okay, right? Well, based on that argument, you could also say that Jesus never condoned it either, so that must mean it's wrong. There are actually a lot of things Jesus didn't say. (He also didn't say pedophilia is wrong, but surely you don't think that's okay.)
But on the subject of marriage, He said everything he needed to say in Matthew 19:4-6. It's there that he reiterates God's design for marriage:
"Have you not read that He who created them from the beginning made them male and female, and said, 'Therefore a man shall leave his father and his mother and hold fast 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 man not separate."
And there you go. In three sentences, Jesus has given the definition of marriage -- which He created by the way -- and anything contrary to that definition is sin, including adultery, divorce, polygamy, pedophilia, and homosexuality. A few verses later, he says that those who are not capable of keeping with this design for marriage should not get married, and he addresses sexual sins in other places like Matthew 15:19, where he says that all sexual immorality is evil.
Understand something else: Whatever is written in red letters is no more important than what appears in the Bible in black and white. After all, 2 Timothy 3:16 describes all Scripture as being from God. And in John 16:12-13, Jesus said to His disciples more teaching was coming through the Holy Spirit, who is God just as Christ is.
So passages such as Romans 1, 1 Corinthians 6, and 1 Timothy 1 which condemn homosexuality as sin are also the words of Christ. The Old Testament, the gospels, and the epistles are all God's Word. It's imperative to receive the Bible this way when we understand the text.