Let's make some Predictions.

Felt like it missed a final kiss 

yes  and EunSung mother is also dead in prison.

 kretuzerwilhelmxiii:

she's not dead

She’talking about what’s lacking 

 miwa:

The only reason for eun-seong evil doing is to get hae in.
To be honest, it's obvious at the end that they portrayed eun-seong as person who is in need of mental health care because of his mother's lack of care when raising him which had made him crazy for love.
Personally I think, mo seul hee (eun-seongs mother) is just another avaricious gold digger who tried her hardest to make money before going insane and losing all sense of reality as not even taking her own son to acknowledge.

 eun-sung death come at the right time; he was just wanting to live his life with her with no matter what it takes. His mother is just a physics' who ran only for mother to make her life worth with gold and secret month. She did this since chairperson was young in his time, she drop his son for own motive. For later, When Seong made her mother dream fulfilled, she gets mad after listening he used to convert all secret fund into dollars like genius month for business. 

It was hyun plans to make him to do to caught in crime, but unfortunately, eon lost his mind since he wanted only Hae-in to stay with him even afte she forgets all memories but when he found about haie didn't forget easily hyun, so he gets made want her to die for only his sake to let hyun suffered. 

Eon mother didn't cry for his cry,  she took all his share and money and wanted to live life in another place. But She didn't know about hyun plan to caught in an act during caurt care. We saw after prison fight, 

She saw outside snow falling from sky and it was clear vision of his son was also die in the snow. She also strapped herself with the food spoon.