Going to see Wicked and looking for Pre Theater Drinner Suggestions
Barbetta might do the trick (on W.46th - Restaurant Row). I haven't been there in a while, but this is an old-school upper end Italian restaurant with candlelight and a pianist and plenty of romantic atmosphere (they also have a lovely garden (went to a wedding there), but not for January!). Not inexpensive, but since you didn't mention price, I assume you don't care.
Your request is much too general. You need to provide specifics so that we can make appropriate suggestions.
1. People's idea of what constitutes "romantic" can differ; therefore, you need to describe the kind of ambiance you have in mind.
2. Must the restaurant be in the Theater District?
3. What cuisines do you prefer?
3. What is your per person budget? And tell us if that figure includes drinks (wine, liquor), tax & tip.