I'm having a problem with my best friend and ex.

So, I wasn't allowed to date in middle school. Whatever. In seventh grade, I met this guy, Francis, and I really liked him and he liked me. We were basically going out. We held hands when the teachers weren't looking, he walked me home every day, we sat by each other all the time, even my step-dad gave him the "If you break her heart I'll break your body" speach that dads are famous for.
About halfway through 8th grade I noticed he was spending a lot of time with my best friend Scarlett. She held his hand when we walked home from school, sat by him at lunch, and was at his house constantly. I shrugged it off, thinking it was nothing. After all, she was really clingy.
Then I find out that she liked him and he liked her. However, she was my best friend and I trusted her not toput any moves on my almost boyfriend.
Well, I shouldn't have because I found out that one of her friends asked her (while he was still with me) if he was going to ask Scarlett out. Francis said he was seriously considering asking her out ASAP.
I asked him to choose and told her to lay off. He verbally chose me but the flirting didn't stop either way. So I broke it off with him.
Well now, most of my friends say it's my fault. I should have just gone against my mother and gone out with him, or Francis would never do something that cruel and I must be lying. My favorite reason for why it was all my fault? We weren't really dating anyway.
Scarlett and Francis expect me to still be their friend, while they're holding hands and calling each other sweetie and babe, and after all they did to me.
I don't know what to do. Do you think I was out of line and should just suck it up? Or do you think I deserve time away from them?