My fiance tryed to drown me.?

I was out swimming with him in this creek near my home. He has frequent heart pains,but today when he grabbed his heart,he glared at me,and then kissed me. And the he grabbed my neck and held me under water.I fought my way back up and I was crying and he said he was sorry and hugged me. And then he did it again.he held me underwater longer and I had to hit him to make him stop. And then he grabbed his heart again,and asked me why I was crying and running away from him. I told him why and he said he didn't. He said he woulndt ever hurt me and before this he hasn't. This is the first time this has happened and I don't know what to do. He also has bad brain damage necause his dad hit him in the head with a metal bat.