A Herbivorous Dragon of 5,000 Years Gets Unfairly Villainized is a Manga/Manhwa/Manhua in english language, Shounen series, english chapters have been translated and you can read them here. You are reading chapters on www.mgeko.cc fastest updating comic site. The Summary is

For 5,000 years, a harmless herbivorous dragon lived a quiet, secluded life. But everything changed when a girl called Reiko appeared before him. She offers herself as a sacrifice to who she believes is the evil dragon, Revandia, in exchange for helping her defend her village from the demon king. Together, the so-called "evil" dragon, devoid of flight or magical prowess, and the enigmatic girl embark on an epic, demon-vanquishing adventure!