Is It because he stole your bestie away from you or is it because he was rude to you once? Before you do anything about this, you need a real reason why you dislike him.
If it's because you just might be a little jealous (and it's okay to admit it! If it's because you don't think he's a nice guy or he's just not someone you would ever be friends with, it's worth trying to smooth things over for your friendship. Source: Shutter Stock Okay, so you tried to get to know this dude and all you discovered were more reasons to dislike him. You don't need to be this guy's best friend - you just need to be polite.
Source: Shutter Stock Remember how I said if her boyfriend is hurting her in some way or treating her badly to do something different? If your friend's boyfriend is abusing her, cheating on her, hitting on you - whatever - talk to her.
Tell her you love her, you don't want to see her get hurt and you can't keep quiet about something like this.
Also, don't gossip about it with other friends - if it gets back to your BFF, she'll flip.