If your spouse has strayed, you might have good reasons for wanting to file for divorce on grounds of adultery -- but doing so might not result in more than some personal satisfaction. Illinois recognizes adultery as divorce grounds, but you could probably end your marriage much more quickly and economically if you filed on the state's no-fault grounds of irreconcilable differences instead.
Effect on Property Division
The Illinois legislative code states unequivocally that courts must divide property in a divorce "without regard to marital misconduct." A judge can't punish your spouse for having an extramarital affair by giving you a greater share of marital property. However, an exception exists if your spouse squandered marital money or assets on his paramour. For example, if you once had $100,000 but your spouse spent $50,000 of that pursuing an affair, it wouldn't be fair for you to come out of the marriage with only a share of $50,000. An Illinois judge could conceivably award you the entire $50,000 because your spouse already wasted or dissipated the balance, and you might have received $50,000 – or half of $100,000 – if he hadn’t done that.
Effect on Alimony
The law against considering marital misconduct also pertains to alimony, called spousal maintenance in Illinois. A judge can't punish your spouse for straying by ordering him to pay you alimony. This doesn't mean you won't receive it – it just means you won't receive it because your spouse committed adultery. Illinois bases alimony on issues such as the length of your marriage, your need for assistance, the lifestyle you enjoyed while you were married, and the earnings potential of both you and your spouse. If you meet these and other criteria, you might receive maintenance, but your spouse's affair won't have anything to do with it.
Effect on Custody
If you and your spouse are disputing custody of your children, the fact that he committed adultery probably won't affect a judge's decision in this regard either. Like all states, Illinois bases custody entirely on the best interests of the child, so its statutes do not allow a judge to consider marital fault or misconduct if it "does not affect the relationship with the child." Unless your spouse flagrantly exposed your children to his affair, his adultery won't affect custody.
Proving Your Grounds
If you file for divorce on grounds of adultery, you might have to prove to the court that your spouse had an affair. Grounds are required in every divorce – the legally acceptable reason you give the court to end your marriage. If you file on fault grounds and if your spouse decides to contest the grounds, you'd have to substantiate your allegation to the court's satisfaction at trial. You'd need evidence such as cell phone bills or credit card statements, or you'd have to hire a private investigator to gather visual evidence of the adultery. By contrast, you don't have to prove no-fault grounds in Illinois, although the state does require you and your spouse to live separately for a time before you can file for a no-fault divorce due to irreconcilable differences.