Agreed - you need to be treated with respect above all else. this guy is showing you none. And it's not about this new girl he's dating - if it weren't her, it would be another girl. A guy who leaves his girlfriend after 8 years when she's pregnant with his child is not a guy you can ever count on to provide you with a meaningful, mature, rewarding relationship, and you deserve nothing less.
This will be hard at first, but you're going to make it through. As the previous poster suggested, surround yourself with good people, close friends and family, and positivity, and marvel at the beauty of life that you're about to witness. Make your life about your son, and live for him and be the best parent he could ever hope for. Work on that, work on you, and the rest of your life will fall into place. Just get as far away from this guy as you can. Trust me.
And also, if you keep your baby, you'll eventually come to a place in your life where you will be okay with another woman holding your child while he's with his dad. You really will.
Good luck.