Dating my ex's best friend

Okay so by the title I am sure you can guess what my problem is, so here is the story. About a year ago, my ex started doing things that I didn't want him to do. He wouldn't stop when I asked him too, I could have stopped it, but I was too scared. We had been broken up for more than 7 months before his best friend and I started going out. And even then we told him before anyone else what was going on between us, we both didn't want him to find out about us on his own. But now 5 months later my ex is wanting to physically hurt my boyfriend just because it's "the worst thing a friend could do to date another friends ex" Yes, that makes sense but thats life and it could be worse, after our break-up I couldn't even look at him I felt like I was going to be sick, and just recently he told me that he still loves me, I know that I don't want to get back with him, because all he wants is to use me. His best friend saved me, it's hard to explain but he did. I just want some advice on how to handle this situation. How am I supposed to let my ex know that we didn't do this to him on purpose? Is there even a way? I am just very confused and help is GREATLY APPRECIATED!!! If you have any questions about something you don't understand then feel free to ask.

The problem with just telling him is that I am afraid that it will make the situation worse, like he will become more violent

Tell him things happen for a reason, and maybe God wanted you guys to get together so your ex has to learn not everything has to go his way.

yup---i agree with that world person--

not everyting has to go his way--

and jsut tell him that what has happenned has happenned--and you'v letten it go--and now you luv his fren--
and if he starts voilet--than i hav no idea what to do-