I told a girl her boyfriend was trying to cheat on her, and now I'm being blamed?

This girl's boyfriend keeps flirting with other girls, scouting for new girls behind her back and everyone says it. My friend told me he was "scouting for hot girls" when his girlfriend wasn't there. I thought it was malicious gossip at first but then when I met him he flirted with me, called me pretty and asked me to go back with him to his place in a sleazy way, to which I said ew no and reminded him he has a girlfriend.

Me and my friend ended up telling his girlfriend in the gentlest possible way because he was doing this behind her back and I thought she deserved better, and she said thank you for telling me. But a week later, apparently she is blaming me for her boyfriend asking me to go back to his place, and is calling me a "desperate sl**."

Apparently she has told all of the girls in our group that I came onto her boyfriend when he came onto me and I said no?

What should I do?

I told a girl her boyfriend was trying to cheat on her, and now I'm being blamed?
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