How to treat chronic mental illness in someone?

Hi doctor,

My mother passed away recently, and I live with my father now. My father and mother had a very tense relationship, and my father even used to hit her during the early days of their marriage. However, they did not file a divorce because they wanted their children, meaning my brother and me, to have a normal childhood. But during the end days of my mother, my father suddenly started taking good care of my mother. After she passed away, I got mentally ill and had to leave my studies and come back home to live with my father. He has supported me since then, and sometimes I do not feel like mother is gone. I do not know how this transformation occurred in him, and I do not know how I should react to this. I do not know if I should believe that he has changed his heart and supported and loved him like I used to love my mother. Please help me see things.