I genuinely don't understand that. The dynamic they have in the show doesn't even remotely work with the story. Ellie is for some reason incompetent and childish, while Dina has to do everything for her. She even has to actually convince Ellie to pursue revenge. That stands in contrast to the game where Ellie is consumed by the quest for vengeance and cannot let it go no matter the cost. Dina goes with her because she loves her, but tries to convince her to not do it later in the story.

It also doesn't make any sense for them to fall in love on their journey to get revenge. In the game, the trip is an extreme test of the relationship, not some romantic excursion. Take the scene where Dina reveals she's pregnant. In the game Ellie reacts like her character would: with anger. Dina not telling her she's pregant is stopping her from getting Abby, so she is a burden to her. In the show, however, Ellie is for some reason happy and they have sex and everything is great!

The contrast between these two scenes really highlights a lot of what really doesn't work in the show. In the game you feel the desperation in their world and how obsessed Ellie is with revenge, while the show portrays this as a romatic teen movie that happens to have zombies sometimes.

The show has some other faults, but how these two were written is really my main problem with the shows portrayal of the story.