Not Stupid, Spook. You are a woman of integrity. It is just a pity your dh could not match it.
You will get through this. It will be painful and difficult but it will get better. You will get through it for your boys first and then for yourself.
Make up your mind not to speak to your dh for a few days and stick to it. Then you will put an end to all this worrying about whether or not the phone will ring. Just tell him no, I will speak to you the weekend after next (or whatever), for now I need some peace and quiet to help me think.
I know if you are anything like me you will be wanting to do something. I always feel better if I have a plan and feel as if I am changing things in some way. It helps me to feel more in control.
But the fact is what you might really need is just to be quiet and still, do the minimum and allow yourself to think about all that has happened, to arrange your thoughts, reason it all out to yourself and just be. Just be. Rest yourself and gather up your energy for whatever your new plan turns out to be. It will all become clear to you just as soon as you are ready.
Give yourself some space. If you find anything that gives you joy, whatever it is - soaking in the bath, attempting to lose yourself in an absorbing book or film, favourite music, walking in the park with your boys, etc, then devote some time for it. You need all the space you can get for yourself.
You didn't get to be a mother of 2 by not being able to manage. You will manage. You are full of resources you may never even have known about before. It is all within you. You will find that inner strength just when you need it.