My ex is horrible

My ex from last year is trying to talk to me again and he was asking me "why did we stop talking" " why do you leave me on open" " next time I message you, you better fucking respond" " look how short you are" while circling around me saying hes trynna square up with me. He's 17 and I'm 15. I got my sister last year to tell him off and he was telling her that he's sorry and that some guys aren't who they say they are. But he's always saying he's a thug. I have a class with him and whenever he walks by he puts his hand on my desk. His sister my age just came to the school and it's odd. He also mentioned he has Spanish class with me in front of her and she thought he was saying I'm Spanish and he told her I'm black and white and she laughed. (She's fully black) my friend was trynna back me up about it. Also all o see on his snapchat story is him smoking, drinking, his football 🏈 gear, etc. a few nights ago I saw him zooming in on someone's gun.