When Jesus had finished saying these things, he left Galilee and went into the region of Judea to the other side of the Jordan. 2 Large crowds followed him, and he healed them there.

3 Some Pharisees came to him to test him. They asked, “Is it lawful for a man to divorce his wife for any and every reason?”

4 “Haven’t you read,” he replied, “that at the beginning the Creator ‘made them male and female,’[a] 5 and said, ‘For this reason a man will leave his father and mother and be united to his wife, and the two will become one flesh’[b]? 6 So they are no longer two, but one flesh. Therefore what God has joined together, let no one separate.”

7 “Why then,” they asked, “did Moses command that a man give his wife a certificate of divorce and send her away?”

8 Jesus replied, “Moses permitted you to divorce your wives because your hearts were hard. But it was not this way from the beginning. 9 I tell you that anyone who divorces his wife, except for sexual immorality, and marries another woman commits adultery.”

10 The disciples said to him, “If this is the situation between a husband and wife, it is better not to marry.”

11 Jesus replied, “Not everyone can accept this word, but only those to whom it has been given. 12 For there are eunuchs who were born that way, and there are eunuchs who have been made eunuchs by others—and there are those who choose to live like eunuchs for the sake of the kingdom of heaven. The one who can accept this should accept it.”

To define this as not being about marriage is absurd.

If you're going to be as pedantic as you have been on the rest of this thread and limit everything Jesus is saying to what the pharisees asked that's not my fault you insist on being that stupid. Jesus regularly touched on things well beyond the questions he was asked in his responses.