If there was one strange thing Haines would consider today, it would be sharing something very personal with Mildred. The story he shared with her was something even Charles didn't know. Haines had never mentioned the woman because he didn't want Charles to blame himself.
When Charles returned from the military, he was mentally vulnerable. Even when Charles got better and started acting like his usual self, taking charge of the company, Haines knew that Charles was simply trying his best to hold on to his sanity. It was when Allison came into Charles's life that the latter's life got better.
Even so, Haines didn't have the chance to tell Charles about that part of his life. He deemed it unnecessary. Hence, he asked for Charles to be transferred to their international branch, which Charles had already considered initially.
Yet Haines told Mildred about it for a reason he couldn't explain. But after hearing Mildred's answer, he finally realized the reason.