He did not actually like Gu Yunhe, but Ruxue was the Phoenix Girl. Ruxue was the Phoenix Girl, and his future queen, so he had to help the Gu Mansion.
If the Gu Mansion flourished, then he would flourish alongside. And if the Gu Mansion failed, he would be humiliated as well.
Gu Zhenkang and Gu Yunhe were both not so smart people. He had been thinking about how to help them, when Ruxue thought of making the princess marry her brother.
Princess Xunyang was not his real sister anyway.
If Princess Xunyang could help to make the Gu Mansion flourish, then that would be the fastest method. That was why he took Ruxue to the court and talked about this with the King.
The King fell into contemplation. He had never met Gu Yunhe, but what Ling said made sense.
Gu Ruxue was the Phoenix Girl, then Gu Yunhe was the Phoenix Girl's Elder Brother.
With this as the background, he could become a great suitor for the princess.