My ex is mad that I’m okay that he’s single...

My boyfriend and I broke up a few months ago (I cut it off because we were both miserable) I hooked up with someone else (WHILE SINGLE) almost because I knew it would prevent me from ever dating him again. About a month or two later after he found out, he decided to have sex with someone else to “get even”. he expected it to hurt me but it didn’t. he’s single and what he does as a single person is his business and shouldn’t be my concern.

He’s getting mad at the fact that I’m not hurt by him being single... this man is 23, has two degrees, works in finance, but is this immature. Why would I get mad at you for living your life? What sense does that make..

Am I wrong?

Edit (to stay anon) he found out bc I wasn’t in town. He decided to tell me to try & hurt me