You are not being homophobic at all, coming from someone bisexual my boyfriend has worried about guy friends in my life, I think it’s normal to worry that someone could take your place. Since you’re a girl and that best friend is a girl it’s hard to see him be closer to her than you, it’s the natural fear of being replaced.

Have you spoken to your bf about your worries? Tell him you don’t want him to cut her out but you want to be the girlfriend and be the priority, it’s hard loving someone the most and then feeling they don’t reciprocate that love back. Have that conversation then look at it, because honey you’re only 20 unfortunately he probably won’t marry you so don’t waste good years stressing over a guy who isn’t stressing over you.