Look at it this way, your ex has shown you what kind of a person she really is. Would you really want to be with someone who would dump you just because there's someone new on the block? It really hurts now but it might be for the better in the long run. There's not much to say about the loss of your father other than I am really sorry. I've never experienced a loss like that so I can't really give any advice but hang in there.
Oh, and hi, I'm one of the aforementioned Newbz.