As a rule of thumb, all newly separated people are broken.  Divorce is emotionally traumatic and the changes are overwhelming.  Relationships fail for a reason, and your first mistake was dating a man who probably had a good hand in killing his marriage based on his immature response to ending your relationship.  If your Mr. Wonderful was really that wonderful, he would still be married.

I worked in family law.  Men are much more likely to move on by finding another relationship than women are, and sometimes we had to legally divorce our clients before their financial or custody issues were resolved so they could remarry.  The fact that he jumped into a relationship isn't surprising.  You filled a need at the time.  You weren't Miss Right. You were Miss Right Now.  It is rare to find back-to-back soul mates.  It is common to want sex and companionship.

Don't waste your energy looking for an answer from this guy.  Dwelling on the past changes nothing.