But it hurt that he tried so hard to be alone

Hello, I have a little problem with the sentence in bold.

This is a story about a young woman and old man struggling for survival on a God-forsaken island full of vicious creatures. A few months before the woman was stranded on the island, the old man's daughter, which is about the same age as the woman, went missing. The woman narrates:

The old man changed once he picked up his daughter's trail. Can't blame him - fathers are built to worry. (...). It was weird that I knew Irina's name but the old man refused to tell his. I think he was scared, you know, of losing something else. So I did him a favor and never told my name either. "Kroshka" was good enough. But deep down I wanted him to ask. I didn't believe we would find his daughter, but it hurt that he tried so hard to be alone.

Could you tell me why she says "but"? "I didn't believe we would find his daughter" and "it hurt that he tried so hard to be alone" seem to me absolutely unrelated ideas, yet she connects them with "but". I'm almost sure there's something in the second part ("it hurt that he tried so hard to be alone") that I'm missing. Could you please explain it to me?