Why did my ex call me a wh*** and say other bad things about me?

So, my ex and I dated for about a month (a month ago) and everything was honestly pretty great. Whenever we first met and were "talking" there was a bunch of drama going on bc of both of our ex's. My ex of 2 years came back in the picture, and his "ex" (the girl he talked to 3 months before and friendzoned him bc she thought he was weird) came back in the picture. Long story short this guy (who I still like, but I've moved on for the most part) broke up with me after saying things didn't feel the same after a fight we had. I understood, and we haven't talked since then. 5 days after he broke up with me, him and his "ex" got back together and have been dating for about a month now. Now, I never talk bad about him or bash him to anyone bc it's just not my place. However, he still continues to talk bad about me bc of that fight we had, even though it's been a month and he has a girlfriend. My friend (who is his best friend and introduced my ex and I to each other) tells me that he always wants to hook up with me still. One time, I (jokingly) said yes and his girlfriend found out, and I ended up looking like the bad person and not him who actually wanted to cheat on his girlfriend. Then, the friend of ours asked if I wanted to hook up with another one of their friends and I sarcastically respond with "Yes!!" and then my ex called me a wh***? The only people ice ever hooked up with or had sexual relationship with are my ex of 2 years and my ex who is talking bad about me. My friend also said that whenever my ex found out that I moved on and didn't care about him anymore (that's not true, my friend just said that cause my ex won't stop talking about me) my ex got sad and said he didn't know how he felt anymore. I'm just confused on why my ex is still trying to hurt me a month later, like I'm not doing anything to him, and he's over here trying to hurt me still.
Why did my ex call me a wh*** and say other bad things about me?
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