The Adoption Of No Fault Divorce In The U.S.
Every U.S. state has no fault divorce, and in almost every state, this is available unilaterally even if one spouse doesn't want to end the marriage. California was the first U.S. state to adopt no fault divorce, which it did in 1970 under legislation adopted in 1969. New York State was the very last U.S. state to adopt "no fault divorce", and it did so in October of 2010.
But in Mississippi and Tennessee mutual consent is required for a no fault divorce to be granted (although, in Tennessee mutual consent is needed only in certain circumstances and a unilateral no fault divorce is effectively permitted after a two year waiting period), and in many states that have both no fault and fault based grounds for divorce, a fault based divorce can be granted more quickly than a unilateral no fault divorce. (Wikipedia incorrectly states that mutual consent is required for a no fault divorce in South Dakota, but lack of mutual consent merely delays entry of a divorce decree in South Dakota in a no fault divorce by thirty days.)
Fault based divorces are not available in the States of Wisconsin, Oregon, Washington, Nevada, Nebraska, Montana, Missouri, Minnesota, Michigan, Kentucky, Kansas, Iowa, Indiana, Hawaii, Florida, Colorado and California.
In other U.S. states and in the District of Columbia, both fault based and no fault based divorces are available, although no fault divorces are more common than fault based divorces in every U.S. state and in the District of Columbia.
All or almost all U.S. states recognize the concept of "economic waste" of marital property. So, if, in anticipation of a divorce or during its pendency, a spouse, for example, destroys property that this spouse controls, or otherwise intentionally or recklessly disposes of it for far less than what it is worth, the loss of value to the marital estate from the act of "economic waste" is charged to the offending spouse.
In some states, merely grossly negligent or negligent conduct can constitute economic waste as well, but that would be a minority rule.
Conduct Relevant To The Best Interests Of The Child
Parenting time and parental responsibilities are universally adjudicated under a "best interests of the child" standard.
So, conduct that is specifically relevant to the parent-child relationship of the parties (e.g. driving drunk with the kids in the car, or not feeding the kids regularly), may be considered with respect to decisions on parenting time and parental responsibilities (a.k.a. custody and visitation determinations), on a case by case, fact intensive basis.
But conduct of a parent that does not directly impact parent-child interactions of either spouse (e.g. an adulterous affair of a spouse of which the children have no knowledge), may not be considered for that purpose.
Marital Misconduct Or Marital Fault Is Usually Not Considered For Child Support
Due to federal welfare benefit legislation that sets requirements for child support laws to make states eligible for federal benefits, child support is determined by a formula (not exactly the same in every state but quite similar in practice) that doesn't consider marital misconduct or marital fault either.
There are two main exceptions to this rule.
First, in a rule similar to the economic waste rule, income can be imputed to a parent of a child for purposes of calculating child support if a parent intentionally earns less than the parent is capable of earning.
Second, the guidelines do not apply beyond a threshold child support amount for high income parents, in which cases the child support award is discretionary and similar to an alimony award which may consider fault in some states where fault may be considered for alimony purposes in those cases. The exact dollar amount of the threshold varies from state to state and from year to year, but is typically a combined gross income of both parents on the order of $75,000 to $200,000 per year.
Marital Fault or Marital Misconduct In Property Division and Alimony Awards
States vary in the extent that marital fault may be considered for purposes of property division and for purposes of alimony awards.
In states that consider fault for property division and alimony, usually both no fault divorce and fault based divorce options are available, and marital fault or martial misconduct may usually be considered for these purposes only in fault based divorce filings.
Colorado and a majority of other U.S. states do not considering marital misconduct or marital fault (other than "economic waste" or conduct relevant to parenting) in either property division or alimony awards.
Some states openly consider marital fault in property division and alimony awards. A handful of states (most notably North Carolina and Mississippi) have "heart balm" torts like "alienation of affections" that effectively allow someone to sue the "other man" or "other woman" who had an affair with their spouse for money damages. Mostly, but not entirely, martial fault or marital misconduct other than economic waste is a permissible consideration in "red states" in the Great Plains, Appalachia, and the South. Marital fault based tort awards are rare but allowed in theory in Illinois, Hawaii and New Mexico, but restrictions on proof of liability for theses torts make it exceedingly difficult to prevail in an alienation of affections case and recover substantial monetary damages. It is also possible to bring these tort suits with a lower standard of proof in Utah and South Dakota, which continue to have actively litigated alienation of affections suits, although the tort is not used as often in these states as it is in North Carolina and Mississippi.
Some states that do not have heart balm torts, however, can still consider martial fault in property division and in alimony awards, at least in fault based divorce cases.
In California, the community property regime does not consider marital fault in property division. This is also true in all other states that have full fledged community property regimes: Arizona, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington, and Wisconsin
California does not consider marital misconduct or marital fault in alimony awards either.
New York State
The legal culture in New York State to some extent probably does implicitly consider marital fault, since intuitions of legal practitioners and judges don't change as quickly as the law does, even though it should not consider this since consideration of marital fault in property division and alimony was abolished as a consideration in New York State in 2010. New York State's common law derived system of equitable property division is much more discretionary than that of California, which makes it easier for fault based intuitions of legal practitioners and judges to intrude on how cases are resolved sub silentio.
But marital fault or marital misconduct (other than "economic waste" discussed above) is not among the factors that may be considered in New York State by statute. Old case law to the contrary has been superseded legislatively.
Appellate Review oF Marital Fault Consideration Is Difficult To Perfect
One reason that pre-no fault practice can have enduring influence on post-fault decision making by judges in New York (most of whom practiced law for most of their careers pre-2010 when property division and alimony awards in New York considered fault), is that there are few effective means of overturning on appeal a decision that covertly considers these factors.
This is because, in practice, it is quite hard to review on appeal an improper consideration of marital fault in a New York State property division or alimony award.
The court has broad discretion to equitably divide property and to make an alimony award, considering fact rich evidence that can reveal marital fault incidentally. And, in a fault based divorce (which still exists in New York along with no fault divorces), the evidence may have even been admitted properly and may have resulted in judicial findings of fact, for the other lawful purpose of determining valid grounds for a fault based divorce were present.
Also, divorce decrees are entered by judges, and for appellate purposes, unless a judge expressly states in an oral or written ruling that an impermissible factor was considered, a judge is presumed to have ignored legally irrelevant evidence presented to the judge in a hearing or pleadings, even if evidence of marital fault is improperly admitted into evidence over the other party's objection, or is admitted into evidence without a preserved evidentiary objection.
Also, often a judge will not make particularly detailed findings of fact or conduct details analysis of the court's reasoning in writing or orally, beyond a bare minimum of factual detail necessary to state what the find decision of the court was in the case and to make jurisdictionally required findings of fact. Judges are busy and they often due the bare minimum of work to resolve cases in ordinary divorces that come before them to decide.
So, usually, the fact that marital fault evidence was presented at a permanent orders hearing in a divorce will not provide a basis for reversing a decision on appeal, even though it is plausible under the circumstances that the judge's decision on property division or alimony was influenced by marital fault.