"Believe the dictionary," is a weird phrase. Dictionary definitions do not attempt to determine reality or separate fact from fiction. That has NEVER been the purpose of a dictionary. Dictionaries describe the way people use words. That's it. There is nothing in there to believe or not believe.
To the extent that a dictionary's definitions are supposed to reflect some aspect of objective reality (specifically, the meanings of words as commonly used), they are separating fact from fiction. It is a fact that "coffee", in the general usage, refers to a specific beverage made from a plant and not to a kind of geological formation. One can conceive of an alternate universe where the opposite is true, but we don't live there.
So there is something to believe, there. You can believe, or not, that the dictionary is accurately capturing what people in general mean when they use a word.
Which, going back to the topic at hand, it does. "Sex without consent" is in fact what most people mean when they say "rape" You
should believe the dictionary if it defines it that way.