My Child's Father is having another baby with his girlfriend

Me and my Daughters Father split last March, so it's just approaching a year on. He left me for this girl he's always been in love with, and now... They've just announced they're expecting August 11th. I'm absolutely heartbroken and finding it hard to come to terms with this. My Daughter will be 2 this coming May. How can I deal with the fact he's having his second child with the woman who plotted for him to leave me for her, and has been very nasty towards me on social media to her friends. I'm sorry if people think I'm being unreasonable, I know bringing a child into this world is a beautiful incredible thing. And I now have a little respect for her as she's a mother to be, and I know how incredible it is making a human-being and raising them. So right now, I do have respect for her in that sense. However, I just can't seem to come to terms with this news. I feel very hurt and can't think about anything else. 

I guess I've always held out hope that maybe we'd be a family again, (silly I know after what he done to me) but he was my first real love. And the Father to my baby. I'm pretty heartbroken