Your question assumes there is a rational explanation, and there can't be. The answer is just what Pelican and tjp have said: he no longer has someone to shield him from the truth, like his family did for years, and this is how he is bound to react.
You need to be proud of yourself for getting him out of the house, and be glad that all you need to do to avoid his harassment is ignore his phone calls.
Hang in there!