I feel for you because your heart is caught up with a guy you thought was available...he may still be but he needs to work out this for himself by taking the time and space that he has asked for. You worry that if you give him the space he will go back to her...if you don't he still may after dragging you through more turmoil.
Let him be, let him sort it out in his own mind. If he comes back he is yours to plan your future with..if not he never was. Better now than 2-5 years later when there might have been a marriage kids and a house!
It won't be easy but you need to cut contact and look after yourself, don't revert to pressuring him.