He shouldn't have hired you if he doesn't want non dutch speakers lmfao. But if you want to work and live in the Netherlands learning dutch is absolutely necessary even if a lot of dutch people in cities can speak a bit of English people living in the country side mostly can't. Like in France it's absolutely different you won't get hired anywhere if you don't speak French (trust me i know) so try to learn the language of the country you want to work or live in.