I see you have improved yourself,by alot if we compare with your previous game "Heat" yet I think story is kinda fuzzy didnt put much thought about it but here is my theory on a short version.
Heat created Light cause of lonelyness,He killed her mother..cat,When the guilt came heavy,he slipped away from reality,Somewhere in the game it mentioned that Heat got"bruses" from her mother,Which child abuse can be result of Schizoprenia,At the time where katherine had a car crash,I think Katherine declined her,and in the result He pushed her..but heat changed his memories he remembered it like he wanted to be,So he put Light in a guilty position,reason of all these things happened to him,but in the end he came to his sense's and decided to end it all..one question who is "Sam" which is mentioned in your previous game