Ok let's assume he is telling the truth. I can't read his mind so I can only assume.
The only way in my opinion to get a decision out of him is to stop the relationship until he takes a decision. Habit and security are strong enemies. He needs an incentive (having you) if he leaves his wife and a risk if he doesn't (losing you). If he needed time, he will come back in a while with a decision. If not, you will know he didn't love you and in the meantime you will have taken care of yourself. It is an ultimatum in a soft shell if you want. You would be friendly but firm.