I acquired Dogmeat as a companion last night. He was with me when I paid for Charon's contract in the 9th Circle(Him killing his prior owner gets me everytime ), and both he and Dogmeat followed me all the way to the Statesman Hotel to rescue those schmucks at the top.

I was under the impression that only one companion was allowed. Was this a glitch of some kind or is Dogmeat allowed to be a 2nd companion? Or is more than one companion allowed?

This is on the 360 version if that helps.