You say he was in a relationship for 13 years. How long was he out of that relationship before he started seeing you? It sounds to me that you've been caught on the rebound. Obviously he was never finished with that previous relationship or he wouldn't be back there.
You shouldn't be confused that they are living together so soon - remember they were together for 13 years. He may say he never meant to hurt you, but that is exactly what he did. Just because someone says they didn't mean to do something doesn't absolve them of their responsibility. He should be the one feeling rotten for dragging an unsuspecting person into his life when clearly he wasn't ready for a new relationship.
If I were you I wouldn't keep talking to this guy until you feel better and are over your loss. It's only going to make it harder for you to get better and feel better about yourself. You
have been given a raw deal and he dealt the hand. He should have done his thinking and worked on his issues
before he put himself out there again. This is not your fault.
As for having absolutely nothing... well you still have your legs don't you?
Seriously though, as I said, he wasn't finished with his previous relationship and he shouldn't have involved anyone else until he knew what was going on. You may still be able to be friends one day, but not while you're feeling like this. Keep away from him, don't talk to him, go out with friends and keep yourself busy. Eventually you
will feel better.