Yes, it's grammatically correct. Let's imagine you have a friend who reads a lot of romantic novels and believes in love at first sight. You could say to her, "You're a true romantic."

Grammar and grammar only We can't say it's wrong. The thing is the whole sentence is odd. Normal when your boyfriend do something nice and kinda romantic you say something like : You're sooo sweet. Romantic often use in written. article, novel describe a he or she like this: He was a romantic at heart and longed for adventure. 他骨子里是一位浪漫的人，渴望历险。 He was romantic with a capital R. 他纯属浪漫派。

Yep it is, also "a true romantic" or a "a hopeless romantic" are really popular expressions. :)