In New York, just as in other states, the time required to get a divorce depends much more on whether you and your spouse can reach an agreement than on your grounds. This isn't to say that your grounds for divorce won't affect the timeline, however. If you file for divorce on grounds of adultery, it will probably necessitate a trial, so your divorce will take longer.
In 2010, New York became the last state in the country to recognize no-fault divorce. New York's no-fault grounds is irretrievable breakdown of the marriage. If you don't charge your spouse with adultery in your complaint for divorce but file on no-fault grounds instead, you could conceivably be divorced in two to three months. This assumes that you and your spouse can reach an agreement regarding custody, support and property, so the court doesn't have to decide these things for you. If you and your spouse can't reach an agreement because he's antagonized over your adultery charge, making negotiations difficult or impossible, your divorce could take one to three years before all issues are resolved by a judge.
Necessity of Trial
In New York, divorce trials address not only disputes about property, support and custody, but grounds as well. Therefore, even if you and your spouse manage to reach an agreement on these things, you'll still have to go to trial if you file for divorce on fault grounds, such as adultery. You must prove your grounds to the judge before the court will grant your divorce. You can reasonably anticipate that preparing for trial will take at least three months, and possibly longer if you're litigating things other than grounds. After your trial, you may have to wait another two months for the judge to issue his written decision as to whether you've proven adultery.
Burden of Proof
New York law doesn't make it easy to substantiate adultery in a divorce action, and you'll have the burden of proof to convince the judge that it occurred. Even if your spouse admits to it, or he simply doesn’t challenge it occurred, this isn't sufficient for a New York court to grant you a divorce. You must supply corroborating evidence as well. This typically involves the testimony of witnesses, but New York courts generally don't place much stock in the testimony of paramours, hired private detectives or prostitutes. You'll also need physical evidence, such as photographs, correspondence or cell phone records.
New York courts generally do not consider adultery as a reason to award additional marital property to the injured spouse. Judges will typically only do this when marital fault involves a high degree of violence or abuse. Your spouse's adultery is not likely to affect a court's custody decision, either. New York bases custody decisions on the best interests of the child, and a parent's extramarital affair would not necessarily make him a bad parent – unless the affair caused deep psychological or physical harm to his child.
You don't have to file for divorce on grounds of adultery just because your spouse strayed. The fact that it happened doesn't preclude you from filing on no-fault grounds instead, or from using other grounds that might be easier to prove. If your spouse flaunted his affair and this caused you to seek counseling or other help, you might have grounds for cruelty. If you file on New York's no-fault grounds of irretrievable breakdown, you usually don't have to prove your grounds at all.