Why is what you believe not a myth?

Last night I remembered a huge turning point in my life. I was 16 and in the car with my then girlfriend who had just converted to catholicism. While I was no longer “born again” I wasn’t an atheist. I had been having a discussion with her about mythology. We were talking about the various Greek, Egyptian, and Norse gods. We both found the topic interesting, and then I made the comment “I think christian mythology is really cool too, I wonder if there is a book with all the various angels and daemons…” At that point she became upset and told me not to call her beliefs a myth.

It killed the conversation, and I didn’t bring this up, but the question hit me like a ton of bricks; “Why is what the Greeks, Egyptians, and Vikings believed a myth, but not what you believe?” I just couldn’t think of how she would have responded. Possibly one of two ways “They just aren’t” or “nobody believes in those gods anymore…” The second response begs the question “so the validity of a belief is based on the number of believers?” This is clearly an ad populum fallacy. If 3 billion people believe lead can float in water, it doesn’t make it so. Same as if a great multitude believe in god, it doesn’t make it so.