You will file a part-year resident return for New York. Since you regularly live in both states, then your resident state is the state in which you have established a "permanent" residence (New York). To determine permanent residency, some things that would be considered are owning a home, where your driver's license is from, and where you are registered to vote.
The instructions below are for moves to another state, but the same rules apply when filing a part-year return for your situation.
How do I file if I moved to a different
state last year?
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