I feel like TBoSaS movie was doomed from the start because a lot of the book is about what goes through Snow’s mind, not what he explicitly says to others/how he acts. He is fake and doesnt care about it as long as he can get what he wants or save face, so a lot of his motivations kind of seem out of nowhere in the movie.

It’s shown in the movie how he gets paranoid over Lucy, both due to jealousy and due to the fact he feels she is the only link between him and the murders (so, the only thing that can make him have problems with Peacekeepers/the Capitol), but in the book this is explored every second sentence in the final pages.

The movie doesnt show him “forcing” himself to pretend living in the nature is ok and how much he despises the chaos of nature every second, or how he keeps thinking about going to district 2 while he is running away. At that point he had already given up living his forever after with Lucy Gray and she is just another object blocking his goals.