Boyfriends best friend told one of our mutual friends he is in love with me!

I’m in a weird spot because he is also now one of my closest friends... I don’t want to tell anyone I know and I don’t want to tell my boyfriend especially. This friend is more like a brother to him. Also he hasn’t ever tried anything with me or overstepped in any way so this information was shocking to me. Do you guys think it’s wrong to not tell anyone? In a way I’m glad I know so that I can be more cautious of our friendship now and make sure there are clear firm boundaries.