What defines a language? In the absence of context, I can't give you criteria for where the line is between a language or a dialect. But that doesn't matter, because the most important definition for "what's a language vs a dialect" is "how is it perceived by the world?". If the entire world thinks that Spanish and Portuguese are different languages, then they're different languages. It's that simple.

This isn't circular because I'm not saying "they're different languages because they're different languages". I'm saying "they're different languages because people say they're different languages".