why? maybe because loss is hard. and sad.
but from what you describe I think he's right whether he was being sincere or not; you are better off not being together.
Even if he is 'sober' for now.... you know from your own experience that recovery from addiction is a long and trying path. Given the history, it sure seems to me from what you describe that you taking time to just focus on YOU and not remain tied up in an unhealthy co-dependent relationship would be in your best interest.