Theologian needed

This is a very dull blog, I fear.

But if there are any theological experts out there who understand this kind of thing, I really would like an answer, or at least an opinion.

Yesterday, when George W. was schmoozing with Pope Ratzinger, he said he agreed with the old Pontiff that relativism was a Bad Thing.

Scarce 50 years ago, when I was at a Catholic school in London, the priest who taught us Religious Knowledge (surely an oxymoron?) told us, among other things, that Limbo existed and that eating meat on Fridays was a sin. Later in life, in the States, friends told me they were taught that the meat rap was, in fact, a mortal sin. I seem to remember it being venial, but that´s not the issue here.

Now, I gather, Limbo either never did exist, or else they have shut it down, and meat eating on Fridays is off the sin list. Am I right?

Because if I am, it appears to be an open-and-shut case of relativism. If believing in Limbo was relatively right then, how can it be relatively wrong today? And what happened to the sinful meat eaters up to when they re-wrote the score?
Are they still doing time in Purgatory? At least until that goes to hell the way Limbo has?

Can a sin stop being a sin without relativism getting involved? Not as far as I can see.

I suppose Galileo was relatively wrong in his day. Maybe, for Ratzinger, he still is.