The Obsessive Best Friend Dilemma

My best friend will call her Sarah, has a bit of an obsession with this boy. Let's call him Brian. Brian is best friends with my boyfriend. Brian has said on a few occasions that he is not interested in Sarah. However, Sarah is constantly trying to encourage us to hang out in a group,. Despite Brian not being interested. And I think it's starting to make him feel uncomfortable. If you have any advice on what I could say to her, please spill. It's a shame because isn't that the dream? That's the dream. She wants to make it happen. You guys are so in love. But she needs to move on from it and have fully supported