That was true. The demon sealed by the Doctor was a major problem, and the Priest would certainly suspect whether the Doctor had been possessed by it. And although the Priest was connected to an Angel, the Deathbringer Angel's power was simply too dangerous. It was perfectly normal for the Doctor to be suspicious of the Priest as well.
Even if the two were willing to share their secrets—which was unlikely—the Priest would still find it difficult to believe that the Doctor could keep the demon under control forever. And Shade could guess whether the Doctor would be willing to trust a Priest wielding Angelic power.
Without Shade, the Doctor and the Priest would have had to keep going out to gather demon or Angel remains themselves. Add the matter of the Chosen Ones on top of that, and by the end, their relationship might have become completely hostile. Something like, "I'm helping you, Bill. Put down the gun in your hand," or, "Priest, why won't you trust me?" would not have been impossible.
"So how did my joining make you trust each other?"
"Isn't that obvious? That strike of yours at the manor, along with everything you did afterward, proved that no matter what happened, you could keep anyone in the group under control. And afterward, you actively involved yourself in everyone else's affairs. Everyone kept benefiting because of you. As long as you're here, everything is manageable. I've even started trusting myself. Everything is moving in a better direction, so there's no need to be suspicious of one another."
The Doctor spoke casually. To him, he was merely chatting with Shade. But it made Shade think of the Sixth Epoch without himself. In those cycles of the Past, Long-Haired Luvia had probably truly reached the end alone.
The