I don't think blaming the friend is a very good idea at the moment... Think it's somewhat inapporopriate, even insulting in a way. Know it would be for me.
Anyway, to answer your question- Of course it's not your fault... I know it hurts, but I'm sure the law is on your side. You didn't push her into the road, you weren't the driver and you didn't make her to stay and chat, she wanted to. It's just the way it turned out and it's so sick and out of your control there's a need to find someone to blame. It shouldn't be you... Her boyfriend is trying to make some sense of this whole event and he chose you as the victim. It's wrong. I'm sure it hurts you just as much as him and being angry with yourself isn't going to help in this case, on the contrary, it'll stop you in the way of coming to terms with her death. I'm sorry you have to go through it, I'd recommend you to stay away from her boyfriend for a while, until things calm down a bit. Hope things get easier soon.