Ex snitched on my girlfriend?

So, My ex and me was talking. And my ex decided to reach my girlfriend and tell her stuff I dont what she said. And my girlfriend just breakups with me just because I talked with my ex after 8 months for 1-2 days just to know how she has been or a friendly convo. My ex was already taken so yeah and I wasn't doing random stuff like flirting with her it was just an casual convo.
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Is there an way to make my girlfriend realize her misunderstandings?
Ex snitched on my girlfriend?
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