The best thing you can do is... Nothing.
Go about your business. Make your plans. Be happy.. I know you probably don't feel very happy right now.. but fake it to make it. Don't beg, don't plead, don't cry for him to be reasonable.. to listen and work it out.. he's probably not capable of doing this at the moment. Plus it only creates more llama drama.. and who needs that right?
Work on yourself. Take any effort you would put into him and the relationship and channel it into you (and your kid/s if you have any). Starting right now.. start taking care of yourself, pamper yourself.. love yourself the way you want to be loved.
Keep contact with your AH to a minimum.. this guy is just going to be a mood hoover. He sounds like a black hole sucking all of your self esteem. Don't give him the negative attention he craves: avoid fighting, blaming. If he brings up splitting/divorce, tell him you didn't want that (if indeed you don't/didn't) but you won't try and change HIS decision... and leave it at that.
Girl.. Go get your hair done, nails done (if you can afford to do so) give yourself facials, make yourself feel good about yourself.. again fake it to make it if you need to.. and then how good you feel will shine through. Careful when you get to this stage though.. seems its like honey to a bee to some As and he may try and hook you back in... now you're all gorgeous and healthy.
*hugs*
Tx