Does anyone else agree with me on this??

So I had a boyfriend a while ago and we dated for a good amount of time. Sadly it came to an end due to family problems, but we are still very close friends now. Well, I dropped one of my classes and had to move into PE and his best friend is in there with me. Well his best friend hangs out with my friend group so I had to chill with him. Nothing wrong with it, he's a cool person. But here's where it goes wrong. My ex's best friend is trying to get with me. He's sent me dick pics, he's tried to get nudes from me, he says he wants to do this to me and do that to me, etc. and I don't like it. I've told him multiple times that I won't mess with him because I don't want drama and personally I don't like it anyways. And I don't know if I should tell my ex what his best friend is doing. Because I know it'll cause a fight. Physically. Any advice on what to do?