Dating ex’s friend?

My ex is super confusing he told me it was okay to date one of his friends. He was the one who brought it up, I didn’t ask about it. So I told him I was interested in his Close friend and his friend was interested me.
We started talking and we went on a date.
My ex was then bothered by this and wanted us to stop talking. I’m so confused by this because my ex says he has no feelings for me. Why would he not be okay with me dating his friend when he SAID I could and when he says he has no feelings for me?
Dating ex’s friend?
Add Opinion