Found: Strange horror novel

In the beginning, the parents become a couple over shared love of Lovecraft.The family is haunted by a being that has both beast and human form. It becomes a friend to the young son of the family and later his lover. The family runs a spook house. The creature comes from another dimension.The father dies prematurely. and the eldest daughter runs away, but is later discovered to be a victim of the creature.

Found it - A Cosmology of Monsters by Shaun Hamill