Should I tell my best friend’s man confess his love for me?

Guys I need advice basically my best friend has a man and they are planning to get marry. Recently I noticed he followed my instagram and I was weird out about it but he found me on my best friend instagram. He start to tell me that he likes me and he doesn’t like my best friend. He said my best friend isn’t attractive that I am, and mind you I was shocked to my core. My best friend seem to be in love with him so much. Should I tell her she wrote all of this? I’m afraid if I tell her she wouldn’t believe me and cut me off. She did something like this in the past and I had to fight for the friendship basically