“I’m a mess,” she tells Tom while he comforts her in one scene. “When I was ill, it felt like I lost something special. I could sing before, I had all these dreams … I’m scared all the time.”
As their relationship grows, Kate starts to see her life in a better light and learns to love herself again.
As for Tom, he suspiciously only appears at the moments when Kate is in the middle of a crisis, then disappears after she resolves them. Which leads us to the big plot twist…
Tom is a ghost! In other words, Kate has been talking to herself all along.