The last time that Buffalo was alone in first place in the AFC East was after week 2 of the 2014 season, when the Bills were 2-0 and the rest of the division was 1-1. Before that, the last time was week 3 of 2011, and other than a few weeks during 2008 (the year Miami won the division and Matt Cassel started 15 games for New England), the only other times since 2001 were after the first two weeks of the 2003 season.
http://www.footballperspective.com/look-who-is-alone-in-first-place-in-the-afc-east/