The baby was the only tie that he had to Killian. The baby was the last remaining piece of him, the shred of his shadow, the only thing that was part of him. Nycta might as well die if she lost the baby.
And the history was not so great, knowing how many babies that he had lost when Rimera failed to deliver them all.
He hated the fact that he might lost this one too.
The regret was getting so strong day by day, he couldn't stop thinking of their last moment together. How he didn't say anything and let him think that he hated him, that he was mad at him.
Yes, he was enraged. He found out that they were unfaithful to him, but then it was not the last thing that he wanted him to know. He didn't want that to be their last moment together.