What should I do next, I don’t want him to go without consequences.

I was in a stable relationship from 1.5 years and me and my partner (P), we were to be engaged. nIn between this period, i made a mistake, I talked to some other guy (O) for 1.5-2 months, things escalated a bit, we went out few times for coffee& dinner and kissed 3 times. I realised I’m wrong here and things are not appropriate, so I left the situation and never indulged even in talking with that guy. (This is back in September 2022)nnNow in March 2023, he approached (P) on Instagram and texted him that I double dated them. O picked P up from his place, used his and mine chats, pictures of outings and went on exaggerating, cooking up lies, I know things would look bad but he made them look worst. I couldn’t say anything because I was wrong and O took advantage of that. O has saved our chats pictures for circulation to my loved ones to seek revenge as he couldn’t handle rejection, he has already destroyed my relationship with P. nO has done this same, to some other girl too.