How about that story where the girl is in love with the guy, and has been for a long time, and he's basically her best friend except that they sleep together? Also it gets more complicated, but there's no real reason to go into that. It's complicated in the way everyone's lives are complicated, with divorces and kids and friends who don't know and damaged hearts and things that haven't been worked through yet and drinking problems and money problems and communication problems.
But in that story, which you already know because we all already know it, the girl is in love with the boy. The boy loves the girl but he isn't IN LOVE with her, for whatever reason, maybe because it's the wrong time or he's not over his ex or she's not the right girl. It doesn't matter. He's not cruel. He doesn't want anything to change because he likes it the way it is, the closeness and the friendship and even sometimes the sex. She likes it too. The sad part is that she likes it in a way that makes her feel like the only right and natural thing would be if he looked at her the way he used to look at his ex, which is also the way the girl looks at him. He avoids her eyes sometimes. The sad part is that she can feel in her little red fluttery meat heart how right it would be if they ate together, paid the mortgage together, slept together every night, were THAT THING for each other.
The sad part is that she knows she should cut it short, should walk away from the eyes that don't look at her that way and the hands that don't touch her that way, but she won't, because she loves him and she hopes that someday he will love her too, that way.