It’s A Little Bit Bunny by Rhea Fox

For the past few months, Nikolai Lorenz’ brain has been a weird place. Things got darker and heavier until the Big Sad drowned out everything that’s good about his life. Not even hockey or puppies can lift his mood anymore and he knows he needs help.
When his therapist suggests forest walks, he grudgingly follows his orders. He wants back on the roster–and fast. Hockey is the only thing he’s good at and his life is even more empty without it.
On his first outing he loses his way in the vast forests of the Fichtel Mountains. The old man who rescues him from having to kip under the stars is no other than the elusive Höimann, a dangerous creature lurking in the woods.
The young human wandering through his forest intrigues Jules so much the self-proclaimed hermit reveals himself and takes him back to his house. For two centuries humans have been too scared to approach him but this one? He treats him with kindness.