Why did Snape always be so dreadful to Harry although he risked his life once and again for Harry? Just because he hated Harry's father?

Yes, he hated Harry's father. And Harry was the reminder that Lily had preferred another man.

Severus protected Harry because of his tình yêu for Lily and of the pledge he had made to Dumbledore when she died - the infamouse "Anything".

What I loved in the last movie is the line added in the script as it is not in the book : "You have your mother's eyes..."

He hated Harry for his looking like James but every time he could see Harry, he could see Lily.

He only risked his life for Harry because of lily.