You may be entitled to relief on alimony, but not on child support. Alimony is based on your ex-wife’s need for support from you. If she no longer has a need, you may no longer have to pay.
In some states, the mere fact of residence with another man is enough. You would have to show the court that they are actually residing together, not just visiting. This could be demonstrated by proof that your ex has given up her prior residence, that she has registered the children in a new school district, or by documentation that she is receiving her mail at her boyfriend’s home. Sometimes it’s useful to hire an investigator to place her there at night over a period of weeks. Investigators can be expensive, so you will want to have the observation take place two days one week, two different days the following week, and two other days a third week.
In other states, you would have to show an economic relationship between your ex and her significant other to establish that she no longer needs support from you. This can be shown by a reduction in her rent expense, joint accounts, etc. Once you can show that they’re living together, many states will require her to show that there is no economic relationship.
The bottom line is that it’s not wise to just stop paying. You will need to file a motion and get a court order. Even if you’re sure your ex doesn’t need the money, it makes sense to pay the support into an escrow account until a judge decides the motion.
As for child support, no such luck. Your obligation to your kids comes from your status as their dad. Mr. Wonderful has no legal obligation to support them. Don’t abandon your role, either emotionally or economically: they may need you more than ever!