Savitar wants to believe. He scans that earnest face for any hint of deception, there is none. Trouble is, he can't remember saying the words. If this Barry was the same Barry he had been he would know. He wouldn't need to trust them and he can't trust them when they all wear the same faces as the people who hurt him in the worst way possible.
And Barry's face has hope, but it is hope mixed with fear. That fear will always remain, Savitar's legacy; the very same he'd wanted to inspire as a God would forever keep him from what he desired as a man. He'll take forever instead, seeding himself into history, never at risk of being wiped out like he had been intended.
Barry Allen wanted to rewrite destiny, it's an irony that's what both versions are seeking, in wildly different ways. Barry wanted to save the woman he loves (to save himself), Savitar just wants to save himself (because there is no love left for him, nor in him). He can't accept the place offered to him, indistinct, tenuous, at risk. A God doesn't hope and wait; isn't weak, open, vulnerable (anymore). He will take his rightful place instead, definitively.