Why are Grinnick and Adalind together?

Because of the baby. According to the relevant information of the American TV series Grimm, Adalin is pregnant with Nick's child, because Nick finally chose to bury the hatchet with Adalin. "Green" mainly tells the story of Nick Buckhardt, the descendant of Green, struggling with supernatural beings in the world. In this process, he and his companions went through hardships, learning ancient knowledge and skills, and at the same time experiencing growth and exploration of the unknown world.