One of the most common questions people ask after discovering infidelity is whether it will "matter" legally. The honest answer is that it depends heavily on your state, and in most places, less than you'd expect.
No-fault divorce is now available everywhere
Every U.S. state allows no-fault divorce, meaning you can end a marriage by simply stating it's no longer workable, without proving anyone did anything wrong. This is how most divorces are actually filed today, even in states that also allow fault-based filings, because it's typically simpler and faster.
Fault-based divorce still exists in many states, as an option
A little under half of U.S. states still let you file on fault grounds, including adultery, as an alternative to no-fault. Where this is available, proving infidelity can sometimes factor into:
- Alimony (spousal support): in some states, a spouse's infidelity can reduce or eliminate their claim to alimony, or, less commonly, increase the amount owed to the betrayed spouse
- Property division: in a minority of states, marital misconduct can be a factor in how assets are split, though most states divide property based on financial and equitable factors regardless of fault
What it essentially never affects
Custody decisions are governed by the best interests of the child, not marital fault. Whether the divorce is granted, and how long the process takes, is also generally unaffected by infidelity itself.
The bottom line
Because the rules vary so much by state, and because proving fault often requires evidence and adds time and legal cost, many attorneys will walk you through whether pursuing a fault-based filing actually makes financial sense in your specific situation. This page is general information, not legal advice. A licensed family law attorney in your state is the right person to tell you what applies to your case.