Wilson's Heart - What is Boris talking about?

Spoilers ahoy.

In the game Wilson's Heart, a demonic teddy bear, named Boris, hunts you and attempts to kill you several times.

He taunts you, saying things like "If your friends knew why you were really here, they wouldn't like you very much!" and "You're not a very nice man, are you Wilson?"

And Wilson never denies it, in fact he comes off as defensive and tries to shove the discussion in another direction more than once. Which directly implies you have a shadowy past that you don't want people knowing about, and Boris (somehow) knows about it.

Not only this, but three times the fact that only Wilson notices Boris is brought to attention; twice with the nurses near the start of the game (before they both are killed by the bear), and once at the very end when talking to Dr. Belasco. This hints at a personal demon.

With the later discussion as to if Wilson had a kid, I thought they were setting up that the bear (Boris) represented some sort of issue in his past with children (possibly the death of his child?). So he's here at the hospital for some selfish, self-serving reason, perhaps to escape this shadowy past that Boris the Bear is referencing.

At least that seemed to fit with the pieces provided.

By the end of the game, however, you discover that you were at a hospital to give up your life in a heart transplant for your sick brother, so that your niece might not grow up without a father. Which is overtly self-sacrificial, and an entirely non-selfish reason for not being at the hospital.

So what was Boris talking about? What's the deal with Boris?