Getting to know that the Lord of Death was most likely truly Lux, was both truly relieving and frustrating.
The additional fact that he was able to fuse with one of his soulbonds made Jason feel conflicted.
He was happy to have more intel that confirmed his theory about Lux being the Lord of Death, but the natural soul fusion was something that irked him.
And this was even more so the case because he recalled the strongest soulbond of Lux.
If his memory wasn't wrong it was probably the Lich, or whatever the existence that became stronger by devouring the souls of others had been.
It was annoying to think that Lux might be able to fuse with this being, and receive a boost in his strength.
What worried him was he had no clue how strong they were alone, either.
As such, his mission became suddenly more difficult than it had previously been.