If your GF likes another guy who would you blame him or your GF?
The issue is not in liking another guy.That is as natural as the word natural can possibly depict.
Even as a married woman U are not immune to developing some form of attraction to another man.
Believe me nobody has a monopoly of desirable attributes.
The real issue wld be what she goes ahead to do about it,and the role the guy plays.Only then can the blame game begin.