1) Learn Torah together! Pick something neither of you ever learned that interests both of you.
2) Explore NYC! There are a zillion places to do and see and many are inexpensive. Take a walk through some of the parks, ride the Staten Island Ferry, go to the top of the Empire State Building. And many great museums have evening hours, with great lectures on interesting topics.
3) Visit different shuls together! There are late minyanim in Brooklyn, Queens, Manhattan, and the Bronx and most of the shuls have a kosher ezras nashim; take the subway or bus and enjoy each others company on the way and on the way home. In many cases there is a shiur before or after.
4) If your rabbis permit it (mine does) enjoy a theatrical performance together! There is some great theater in NYC and is isn’t anything like the pagan rites Chazal complained about.
Have a great time!!!