The affair between Morrigan and Cu Chulainn, while not common knowledge, was hardly a secret.
Ever since Cu Chulainn returned from the Shadow Realm to Alster and made a dazzling display of his prowess on the battlefield, he had caught the attention of this goddess.
Morrigan had once boldly professed her love to Cu Chulainn.
Morrigan claimed she could bring victory to Cu Chulainn, hoping to gain his love in return, but Cu Chulainn recklessly asserted he didn't need anyone's help in battle, especially not a woman's, and showed a contemptuous attitude towards her charms. Thus Morrigan became his deadly enemy.
Despite numerous confrontations between them, in which neither gained the upper hand, Morrigan was a deity, and Cu Chulainn was no ordinary man. The Shadow Leader didn't think he could survive against her.
Therefore, the mere sight of her alone completely robbed him of his will to fight, and he didn't dare to show his face in front of her.