So at school, a girl named sarah has a boyfriend that wants to beat me up. For no reason at all... I haven't done anything. So a few days ago me and my friend braiden were joking about in the hallway and he takes me down and then sarah turns around and says hahaha you just got taken down by braiden and I'm like hahah shutup ahha and then next thing I know he wants to beat me up. Ive been worrying about it all this week then after school, I got a text saying is it true you told sara to go kill herself so I was like no so I talked to her after school and I said I didn't say that and she said OK I will tell my boyfriend... only 1 problem... He is coming to our school and is going to be in my class on Monday... I don't know what to do.

Tell the principal of the school. Fighting is a very serious thing, and threats are as well. Let the principal handle this, that's what he/she is there for.