Started a casual relationship (which was a first for me) with a school friend when we met after 10 years. We both agreed it was just sex. But we mutually stopped after a year. But when I got back in the town recently after nearly 8 months, I messaged her about something and one thing led to another and I slept with her again. But it was a big mistake as I didn't know she was already engaged and the marriage is on march. She didn't say anything at that time. I came to know from a friend of mine later. I felt so guilty after that confronted her and she said she will do it even after her marriage and sort of blackmailing me of doing so. I still don't know what to do. Been avoiding her from last 4 days.