Traditional NTR often ends with the female character hollowed out. Here, Riku remains "yasashii" (kind) even as she cheats. She still cares for her boyfriend’s feelings, which generates guilt sex —she sleeps with the antagonist and then returns home to hug her boyfriend tighter. This psychological conflict is the core of the narrative.
If you want to delve deeper into this series, I can provide a breakdown of or look into the original manga source material details. Which area Share public link name: kimi wa yasashiku netorareru the animation