A ghost. Preston had seen those, in his time. First Errol, then Brandt. He wasn't actively searching for Mary's face in the crowd should she come back to haunt him too, but he found himself looking nonetheless. Finding her would be different from finding the Clerics - with Errol there had been guilt and pain and loss. With Mary it would somehow be more than that. So while he could begin to understand the depth and magnitude of the burden that weighed her down, it was something he did not wish to dwell on for too long.
Preston hadn't taken her in out of pity or charity, nor would he confess to have done it out of love. He did care for her deeply, and their relationship transcended any traditional, conventional notions of 'romance' that Preston envisioned. It was love - unlike the way he loved his children or the women he burned in Libria, but still love - just not in a way he could easily explain.
"He seemed to want to validate his feelings with who you were before," was how Preston finished her sentence. He had encountered the other Evey, who must have not endured the hardships they had faced on the island and did not bear the scars of grief on her face, and it wasn't difficult to piece together a puzzle that had, up until now, been floating as unconnected but related pieces.
"I am not the same person I was before I came here. Nor am I the same man who watched my wife burn and felt nothing but betrayed. It just so happens that we inhabit the same physical body. I know nothing about this man, but I know that if he genuinely cares for you, he cares for the continuity of you, not a snapshot of you at single moment in time."