In the Hellboy film series (1& 2), Liz has a romantic relationship with Hellboy, becoming pregnant with his twin children. However, in the Hellboy comic books Liz and Hellboy are just friends; there is no hint of a romantic relationship between the two of them and she is more like a little sister than a girlfriend. (Source:Wikipedia)
Did they change this in the movie just for the sake of a love story or any other reason?