Man returns to his father's cabin which has been abandoned. He discovers some type of fantasy kingdom, falls in love with this fantasy female girl (like dryad or Nymph or something).
Someone ends up attacking or killing the girl and he has to go in track the bad guy down. The bad guy ends up being his brother who he's supposed to kill or something like that.
Sorry don't know how long ago it was published, I read it in prison like 15+ years ago, it looked like an old book, and didn't have a cover. Some of the details could be off also but that's the gist of it, I think I remember something about a tree growing in the middle of the cabin/house