Why did this girls boyfriend flip out on me?

I recently informed a girls boyfriend of her behavior behind his back towards me. He always seemed a bit suspicious of our dynamic. He even bought the same chain I wear, copied some of the slang I use, and would constantly kiss my ass. Anyway the girl and I had a falling out after I confronted her on her behavior. Thing is, her boyfriend is like the nicest guy in the planet and everyone has referred to him as a “golden retriever”

A few months later I texted the boyfriend a long message about his girls behavior. He then basically claimed that I was the one tryna fuck her the whole time and how he was planning on texting me to interrogate me so he was glad that I texted first and that the only reason he didn’t send me to the hospital was because she stopped him. Then he told me that he feels bad for the next couple that encounters me that doesn’t have the “strong level of trust” they have between eachother and then he called me a pussy lmao. Also claimed that the only reason he didn’t “cave my face in” is because he’s a “caring, loving bf” and didn’t want to look jealous. So I sent him screenshots and told him to check her phone to verify everything. It’s been 2 days and he hasn’t opened it

Why did this girls boyfriend flip out on me?
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