I'm afraid you are asking the wrong question: how could we ever know his 'why'?
We could never know that and you could never know that too.

But asking yourself why is a good way to be still entangled in this situation, without getting out.

May I change your question into: is this relationship safe and good for me?
This is what should keep you busy, not his problems.

Sorry if I sounded a bit harsh, but that is what these people do to us: they put themselves and their lives in close up, meaning that they are the only important part in the couple. And little by little we may be induced to think so too.
So please don't think about his problems and his reasons.

Is this relationship safe and good for you?