AITA for taking my ex-wife back to court after she asked me to help support her stepchildren?

My ex-wife and I have been divorced for five years, but I still pay her child support—even though our two kids now spend most of their time living with me. I never questioned it. I make more money, our kids still spend time at her house, and keeping things peaceful between us mattered more to me than going back to court over money. Then she remarried a man with two kids of his own. When I paid several thousand dollars to send our children to a summer program, my ex asked me to pay for her stepchildren too because she didn’t want the four kids in her house having different experiences. I said no. But her request made me look at our original custody agreement for the first time in years—and realize I’m still paying child support based on a custody arrangement that doesn’t exist anymore. Now I’ve spoken to an attorney, and there’s a chance my payments could be reduced or eliminated completely. The problem? I was perfectly willing to keep paying until she asked me to help support her new family. So would I be the asshole if I took my ex-wife back to court to end my child support?