My friend's crush faked cancer to reject him

One of my closest friend started liking this girl and then fell in love with her a year ago, the girl was giving mixed signals, I liked her at first but one day she said "we shouldn't be friends anymore" to him just because her mood was a little off, later she said that she had period mood swings to justify herself because my friend was very hurt. That's when I started to dislike her, soon my friend madeit clear that she can take as much time as she wants but he can't just stay friends with her, she was making up excuses and she started fighting and all, and mid argument she said that she can't date him because she has cancer, now I was very suspicious of this. Me being someone who has read numerous articles related to cancer and has experienced 2 of my loved ones dying of cancer in the same year, I was very offended. I knew she was lying, I didn't say it to him directly because he would get mad at me, so I made him ask her questions and then I knew it, I just couldn't get the courage to tell him. This went on for weeks and then they got close again, one day she says that she doesn't have cancer and she never did and that she can't be friends with him neither date him and that she was just using him for his money and for passing her time. My friend was very heartbroken and he has completely cut off himself from everyone and has been isolated for months.. How do I help him out