What happends if...?

What happends when your bestfriends girlfriend thinks you are after him? What happends when she decideds your a bitch, a slut, a man eater? What happends if he doesn't know how badly she treats you? Do you tell him? Or do you just pretend it doesn't bother you? What do you tell him? "oh yea by the way your girlfriend is a bitch, and I don't think she's the best of people for you". But does that just make it seem like I want him? And that I'm lieing? Because I'm not, he's my friend, my very best of friends, and I don't want her to hurt him, because he's like my brother and I don't want him to hurt. For something I did or said. What do I do?