"how do I learn to shut my feelings off ?"

You must convince yourself of the truth with this man. He never loved you nor cared about you. He is only sad for himself. He wishes to punish you now for daring to leave him and soil his fragile false self. Whether he can help it or not does not matter. He is now out of control. Leaving him is the most caring thing you can do, believe me. One threat of physical harm is one too many. Get authorities involved.