That was certainly fast. Police have arrested Bernard Bellamy, 20, of Oxon Hill, and charged him with first-degree murder in the death of Valicia Demery, 19, whose body was discovered early on Sunday on a jogging track behind Forestville Military Academy, the Post is reporting. Bellamy was taken into custody at West Virginia State University, where he is a sophomore. The suspected motive is painfully obvious: Demery was four months pregnant, and Bellamy was…