How should I handle this situation my friend cheated on his girlfriend with my sister?

I am not happy with him at all…. Not only because his girlfriends sweet but also because he has dragged my sister into this. It’s of no fault of my sister she was led to believe he was single. When she found out he had a girlfriend she told me what had happened.

She’s worried because she doesn’t want to be looked at as a monster especially because things like this spread around school fast. She doesn’t want to look like someone who intentionally slept with someone who was take.

I confronted my friend because he cheated on his girlfriend and really hurt my sister. He made me feel like a bad friend basically and was begging me not yo tell anyone. “Oh bro it’s not that deep. It was one night and by girlfriend been moody as hell bro” and I wasn’t buying his shit.

I feel like I should tell his girlfriend myself. Before things get any worse.

How should I handle this situation my friend cheated on his girlfriend with my sister?
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