Oh sweetheart I am so sorry to hear your news, really sorry. Lots of us understand what you are going through and we know how badly something like that hurts when you are pregnant. You MUST be strong about this though okay. He is not a nice person. Any man that posts a picture on facebook of his new girlfriend being pregnant whilst the other one is also expecting, is a big shit of the highest order. Look, you know what he is capable of (abandoning you and baby etc, etc) so his personality is deep down crappy okay? This means this poor other girl is gonna get his rubbish behaviour at some point but you are now free of that. Don't for one second think that
you are any less of a person because of what he has done, because that's not true. If I was his girlfriend, I would be seriously questioning in the back of my mind why he left another girl pregnant and that would make me very uneasy. You are in a better position now as you are free of him and his selfishness.
You need to just get all the hurt and tears out first, eat buckets of ice cream, watch sad movies , whatever releases all the emotions and then quickly brush yourself off and think of all this as a fresh, new start and a great future with your baby and the man in the future who will love you loads and take care of you both. Gived yourself time, as time will truthfully heal all wounds and be good to yourself.
You are well rid of a man like your ex and one day you will realise that, maybe not for a while as it's raw, but one day you will look back and be thankful you are not with someone like that anymore.