You are not legally obligated to support her. If a divorce is filed the court could make alimony retroactive.
In New York, this type of substitute motion is called an "Order to Show Cause." An order to show cause can be heard anytime the court directs, even fewer than the usual eight days, and even as short as a few hours later, if the court is convinced there's a real emergency.
While waiving spousal support is legally acceptable in New York, the agreement should not be "unconscionable", meaning grossly unfair. Courts will examine the fairness of the agreement at the time it's enforced, not just when it's signed.
The best way to avoid paying alimony in the event of a divorce is to sign a prenuptial or postnuptial agreement. These agreements, once seen as unromantic, now serve as a strategic way to protect individual assets in case of separation or the need to dissolve the marriage.
In New York State a married person may be legally responsible to provide for the support of his or her spouse during their marriage, if that spouse lacks sufficient income or assets to provide for his or her own reasonable needs.
In New York State a married person may be legally responsible to provide for the support of his or her spouse during their marriage, if that spouse lacks sufficient income or assets to provide for his or her own reasonable needs.
In New York State a married person may be legally responsible to provide for the support of his or her spouse during their marriage, if that spouse lacks sufficient income or assets to provide for his or her own reasonable needs.
 
                    