Another 'voice of experience' post here
Firstly - I am so sorry you are going through all of this. It is incredibly painful and no matter what the final outcome, it is a life changing event.
Things probably feel very confusing at the moment and until the 'story' stops changing and settles down it is nigh on impossible to really be able to deal with everything and process what it all means to you.
On that basis, all that I think you need to do right now is just concentrate on riding the rollercoaster of emotion that will hit you over the next few weeks/months. Right now you don't need to make any long term decisions - so just park that for now. Once the pendulum has stopped swinging and comes to rest on the side of staying together or the side of splitting up, then you can take that decision, but that is a long way in teh future right now.
Try to suspend the future and live in the moment, that might give you a little bit of respite from the collapse of the future that you thought you were going to share, and allow you some space to build a new vision of the future.
Yes your DH is a knob, but he is far from teh only one! Just concentrate on looking after you for now. Leave him to sort himself out - make him take responsibility for himself and his own happiness - don't try to make decisions that involve his happiness in the relationship - think only of yourself!
You do have choices and you need to take time to make sure that you make the right choice for you - not for him