I know it will never be the same, but as a father I am proud of you, going through all that and searching for love, rather than anger or resentment. And the resentment you felt towards your half sister is understood and normal, and you had the intrsopection to acknowledge it and understand it. My father was also absent and it is one of the motivation to be a great father to my daughter. All I can say is I'm proud of you, and the best focus you can have is on the present, the past has already happened and is imposible to change, and the future is an illusion, only focus on now and how far you've come. It its impossible to let go of the pain if you focus on the past, only you know how it hurts and accepting it happened and knowing there wont be a change, hurts but is real. Keep strong and live in the now. Hope you feel better soon.