First off - congratulations!!! You have a little life growing inside you right now getting ready to be your son or daughter :-)
I had a surprise (but much wanted) pregnancy and both DP and I were in shock and quite dazed for weeks afterwards. I also used to be married and my ex decided to just leave one day when I was at work so I came home to find he was gone and it took weeks for the shock to wear off! Looking back on it now I smile and think it was one of the best things that ever happened to me. He vacated the space I needed to feel
better about myself and made room for a lovely, kind and gentle man who I met less than a year later.
Anyway - the point I'm trying to make is you're digesting two huge life changing experiences in a short space of time so whatever you feel is completely fine! Feeling numb is your body's way of coping with the shock. Later you'll feel every emotion under the sun. It has no bearing on you as a mother or how much you are going to love your little son or daughter when they make their appearance into the world.
Emotionally, I suspect you're feeling quite scared and overwhelmed by it all. However, rationally my not so humble opinion is that if he's the kind of man who leaves a marriage without having the basic decency to tell you and offer an explanation then I think it's probably good that he has done a runner and you're going to be better off without him.
It will be challenging but you will cope and there are happier times ahead for you and who knows who you might meet in the future.
Do you have friends and family around you? Do they know what's happening? Telling them is probably a good idea so they can support you.
Also, putting my practical head on - get legal advice now and if you intend to divorce him get the wheels in motion as you'll want your finances and things sorted out sooner rather than later if at all possible.
Congratulations!!! What a crazy time for you but you'll look back on this in years to come and hopefully see it as the start of better and happier times in your life.
Roo