I think the concept of loyalty has changed somewhat over the years. I think once a player has moved for a fee to their 2nd club at the same level where there at, e.g. 2 Premier League clubs, he's never going to be 'loyal'.
For example, a youth team prospect who works his way into the first team and stays until a big money move comes in I'd still consider a loyal player, and also he'd be loyal to his new club provided he stays for many a year, or until his contract runs out. But if he makes a sideways move to another Premier League club, he'd just become a normal ("mercenary") player. For real life examples of this I'd say Michael Carrick, Frank Lampard, Didier Drogba, Alan Shearer etc. I know it's all subjective, but to find truly 'loyal' players nowadays is hard. Money talks :/
There aren't really any mercenaries any more, it's the norm rather than the exception that players will have at least half a dozen clubs under their belts before they retire.