I'm thinking bad about my friend for talking with my boyfriend and talking to him all through 6th period
Are you sure? What were they talking about?
My friend was persuading my boyfriend to leave me.
I can't believe your friend would do that to you!  Do you even consider this person a friend anymore?  Because you shouldn't be friends with someone who's going around undermining you like that.
I can't believe my best friend is going to make a move on my man.
I can't either, that is very unfortunate for your relationship! I believe you should confront something like this right away before it gets worse. You don't deserve to be back stabbed by a friend like this, so it's best to leave them.