You know what, I think he just wanted a change. When you work/play in one place for 10 years you can get the itch to check out something new. He also seems to like the fact that he will be closer to his family in Miss. He owes the Bills nothing, they are the ones that didn't want to continue under his deal. It's a business and the door swings both ways.
There shouldn't be animosity toward a guy that gave most of his career to the team and the city, likewise there should be no animosity from Moulds.