For me grammar has always been the hardest part. No matter what language I study. Until you understand the logic of the language, the system behind the grammar rules, it’s gonna be hard. Even English, which is considered the easiest language. By the way, I find simple materials like https://promova.com/english-grammar/comparative-adjectives-in-english really helpful. Everything is explained clearly and presented in a way that helps you actually get the idea, not just memorize a rule.