？
Are you seriously telling me you love me?
Literal
Seriously [means-で] me [about-のこと] love-[ongoing-ている]-[colloquial-quotative-って] say-[question-の]?
Several colloquial features stack up. 本気で ('seriously') uses で for manner. 私のこと ('about me, the matter of me') is a common way Japanese expresses 'me' as the object of feelings — emotion verbs like 愛する, 好き, and 心配する often pair with のこと on the beloved/worried-about party, rather than taking a bare pronoun. って is the colloquial quotative particle (contracted from と). ~というの (here ~っていうの) is a rhetorical or challenging question-ending: 'do you mean to say that...?' — often incredulous or confrontational.