AITA for divorcing my wife after she got pregnant in the open marriage I agreed to?

I spent years thinking the worst thing that could happen was losing my wife. I forgave her for spending my savings, tolerated the yelling, and even agreed to an open marriage I never wanted. Then in our fourth year of marriage, she sat me down and told me she was pregnant. The baby belonged to her ex. She thought we’d figure it out together. She thought I’d stay. After everything I’d allowed throughout our marriage, she had every reason to believe I would. But she finally found the one thing I couldn’t accept. Now I’m divorcing my pregnant wife—and she’s reminding everyone that I agreed to the open marriage in the first place. So, AITA for leaving? #AITA #RedditStories #RelationshipStories #Marriage #storytime