I can only speak for the Province of Ontario, where it is not a factor. Edit: Did some digging. It seems it CAN be brought into play, here in Canada, but only to initiate a divorce ( with proof), not for any gain in assets or custody after the fact. Thanks for pointing out that the Divorce act covers the country as a whole. I recently went through all this but went the no fault route. Total cost 200 bucks, all in. :)

I think most states are "no fault" states now. They don't take into consideration the reason for divorce in the financial part of the settlement. And so long as it didn't drastically affect the children, they don't consider it in custody either. You'd have to check each state to be sure, but I know Washington and Oregon are no fault states.

Fidelity may not be considered in the settlement, but it plays a very important part, considering the totality of the divorce. daily, judges sit and listen to divorce cases, where one partner has cheated on the other. i cannot help but believe that the fiedelity would not play a part in a judges decision and final settlement. believe it or not, infidelity still plays an important role in judges decisions. one way or another.

I can only speak from my own experience, in the state of Massachusetts, USA. Massachusetts is a "no fault" state, and the state's family law does not take fidelity in a marriage into consideration when a divorce is granted. This is also not something that is considered in the terms of a divorce settlement (or so they say...who knows what individual judges actually do!)

People can talk about what's legal and what's not. But, realistically and regardless of law, in divorce cases, they mostly consider how the spouses acted within the confines of the marriage. Specifically how they acted towards one another. So, fidelity does count, but only as an indicator of general behavior. "He cheated, She didn't", and fidelity is a plus for her. "She left, and He found someone else", and fidelity is supplemented by the larger issue of abandonment.

This is written as a supplement to another answer dealing with this legal issue in Canada. Divorce is a federal responsibility in Canada, while family law falls under provincial jurisdiction. They are quite separate legal processes. There is a one-year waiting period after the application has been made before a divorce can be granted. During this period, the couple must live separately. However, they are allowed to cohabitate for a limited period of time to attempt a reconciliation, without resetting the one-year 'timer' back to zero. A decree nisi is first granted, followed by a decree absolute 30 days later. The divorce is not considered final until the decree absolute has been issued. Therefore, the typical divorce process takes 13 months to complete. However, there are certain conditions under which a divorce can be granted immediately, without needing to wait 12 months. One of these conditions is legally-acceptable proof of infidelity. Therefore, a divorce could technically be granted in one month with absolute or uncontested proof of infidelity. In practice, however, it takes somewhat longer because of the need to schedule the hearing in a federal court, which does not sit on a daily basis. The division of assets, provisions for the care of dependent children, and other matters are handled in a provincial family law court. Family law clearly spells out the process by which property must be divided and many provinces have guidelines for setting the amount of child support. These are the two most important issues in a divorce. Since family law issues are settled independently of the divorce action, the issue of fidelity is rarely raised in family law court, since it has no bearing on the way in which the division of assets and child care are handled. Judges who stray from the provisions of family law and show a bias against a person who has committed an infidelity can have their orders overturned on appeal. Family law does not differentiate between those who divorce for reasons of incompatibility and those who divorce because of infidelity. It is usually not necessary for either party to be present in either divorce or family law courts in Canada. Neither my ex-wife or I ever attended any court appearances during our divorce. I know that most lawyers prefer it this way and I suspect so do the judges.