My ex firmly decided no kids before I was ever in thhe picture because he had a kid out of wedlock and one was enough for him. I committed to that until he suddenly told me he changed his mind after a year+ of thinking on it sporadically by himself and NOT to his wife. It felt like a betrayal that he didn't share his thoughts as he was debating with himself on an issue that would affect both of us for more than a year... It also killed me that after ~2 years of killing my own desires to have a kid and grieving over the process because I loved him so much and wanted to be with him even if it meant sacrificing having kids, he can just flip his decision and wonder why I am not okay with that.

Tell her, soon. This isn't a you issue, it's an us issue and she deserves to get a chance and time to think about it too.