How can I stop my exes from brainwashing my girlfriend to turn against me?

We bumped into my exes at my friend's wedding. It was awkward as they gave me a cold stare. They wouldn't move on from the past until god know what will make them pleasant. My girlfriend went to the restroom and exes goes in as well. She wasn't come out for about half hour, so I decided to walk in ladies room to find her. When I came in and seen her talking with the exes before they stopped as I appear. As they left, I asked her if they goes gang up on you or something. She denied it and say that they wanted to warn her about me.

How can I stop my exes from brainwashing my girlfriend to turn against me?
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