Why did Erkang say he couldn't marry the golden lock in Princess Zhu Huan?

In the first part, when the emperor was assassinated, Wei Zi, Swallow, Emperor, Yongqi, Erkang and Ertai were patrolling, and Wei Zi blocked the emperor. When he drew his sword, Wei Zi thought he was going to die, so Erkang accepted the golden lock, and Erkang agreed. In this way, the golden lock was promised to Erkang. But Erkang only has Wei Zi in his heart.