Trust is a prequisite for betrayal
He's your Inquisitor... Respect him!
He is your Inquisitor. Member of the Ordos Hereticus. You are in his employ. Thankfully you have a reasonably generous Inquisitor. He has always seen to it that you have any ammunition you need, and clearly has more resources at his disposal than is directly obvious.
Inquisitor Grant is known by many, including many other Inquisitors, and even some Rogue Traders.