My friend likes my boyfriend

My friend that I've known for years likes my boyfriend. I know this because she told me. I know that he doesn't like her like that and I trust that he won't try anything with her, but I feel like the more persistent she gets as her crush grows, the more he'll start to think that they have more in common than we do. I love him so much and I don't have very many people that I'm close with, I don't want to lose him. I just don't know what I should do.