I laughed at her with him now she's laughing at me with him. Why is she being spiteful?

My boyfriend of seven years Baby mother posted a video recording online of him talking about me to her. On the recording; he told her that he was never with me, that I'm bisexual and probably want to sleep with her. (She told him I've been watching her in public for two years.) so he said, "that's stupid. It's my fault for letting her contact you. she shouldn't be watching you. She's weird" just talking badly about me. The last recording she posted online: she said, "you laughed at me , now I'm laughing at you".

Why is she being spiteful towards me?

I laughed at her with him now she's laughing at me with him. Why is she being spiteful?
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