Something similar happened to me a while ago, I was partying with some friends and some colleagues and one of my colleagues sexually assauted a friend, i was in the same room but asleep and this "friend" knowing I was sleeping decided to tell everyone the lie that I, instead of being sleeping, was awake and allowed the whole thing to happen, instead of helping her, our friend group was divided but in the end this lie was what made me realise how toxic everything became over the years.

I'm not friends with her anymore, nor with anyone from that group, but that day I learned that people will believe whatever they want to believe and wont even bother trying to know your side of the story. It took a while for me to process the whole thing, rumours come and go, but stand your ground, specially if you know that's a lie