"No, he is not my new boyfriend."
Translation:No, lui non è il mio nuovo fidanzato.
That works too. Qualifying adjectives (red, yellow, new, old, tall, young) can come before or after the noun, but often when they come before they have an emphatic role, so you're usually safe with the noun + adjective combo (like here!)
There are a few cases in which the placement of the adjective is everything: it either changes the whole meaning of the sentence, or sounds plain wrong
- l'impero romano: just sounds funny the other way around
- bella vita: a saying you won't hear the other way around
- vedono una donna grande: they see a big/large woman
- sei una gran donna: you are a great/fantastic woman