I would recommend counselling, and maybe that will help him to move on.
It was 2 years ago, and failing to move on, could be a cry for help. Stay strong, and hope that time heals his wounds.
Be supportive, as best you can, and let him know whilst you want to see him happier, as its intoxicating your relationship him holding onto the pain of the ex, and its affecting the progression of your relationship.