I would say consider his feelings on this a bit. A suprise kid comes up out of nowhere, and suddenly he has another child, another mouth to feed, another responsibility. I'm sure it causes him as much stress as it does to you. Really......do think he WANTS two baby mamas? Do you think he WANTS to pay extra child support? He may say he's fine but maybe his way of coping is just getting on with business, and you making it into a bigger issue is probably pissing him off.
He's right, you're either with him on this journey or you're not. If it's too much drama for you, then you're both better off separate. If you love him and are willing to see him through this, then do it and stop feeling 'animosity' towards him. It's not like he cheated on you and got a girl pregnant. If you know that you can't deal then leave him. It's as complicated as you want to make it.
Live as if you were to die tomorrow. Learn as if you were to live forever. - Mohandas Gandhi