Magda, are you comparing adjectives with adverbs?
For example, you can say he is happy, happier, or happiest. But if you say "He is happily married" you can't say "happilier" or happiliest." You have to modify it with something else like "even more happily."
That project was big. That one was bigger. That was the biggest. (Three forms of the adjective "big.") But take adverb "hugely." The project was hugely successful. But not hugier successful or hugiest successful. (That project was even more sucessful and other one was the most successful of all.)
Does that help answer your question?