Mental Harassment

There was a girl who loved me severely and would always stalk me online out of obsession. I was not at all interested in her and asked her to concentrate on studies, but she would never listen. There was a boy who was a close friend of mine with a cheap character of chasing girls, who also ended up discontinuing his studies. One day this guy texted her on Facebook and also took her WhatsApp number and tried to spoil the relation, but knowing his character, I asked him to keep the girl if he wants. Months passed and I knew they were getting close behind my back but I completely ignored the issue and the girl as well, but she would not stop stalking me. Finally when the boy thought I came to know about their secret relationship, he played a lot of games and we had a lot of quarrels but I told him to keep her, but the girl again chose me. Few days pass, I got a call from that girl around 11pm and the guy was on the phone and said he was having sex with her and asked for my opinion, he did the same thing on text before that day. He is still texting to my other friends on FB and telling horrible made up stories about me. Could you please tell me how to handle this. It comes under IPC section 504 right.