Do you think he is being an a$$?

He is saying he may be considered a Greek if people think he blushes. The Greeks have long been a known as overly sentimental, unrealistic people (such as people who believe there is a 400-year-old man who turns to sparkles in the sun waiting just around the corner to sweep them off their feet). It is an insult, and your ex-boyfriend does not want want to be ociated with that type of personality.