The Bonds That Tie Us is a somewhat adversarial, multiplayer relationship rpg. Notably, it's not necessarily about romantic relationships---the PCs could be a high-school friend group, or business rivals, or the like---and the tone changes significantly the more distance you get from a conventional romantic setup.
The PDF is 15 pages, with a clean and easily readable layout and no illustrations.
For mechanics, Bonds uses a single d6. Player characters have a Stress rating, which can increase, and altruistic actions need to roll over Stress, while hostile actions need to roll under it.
Gameplay is segmented into chapters, but the book doesn't spell out particular events that need to happen in each---or ultimately how many chapters there are in a story. In that sense, Bonds is more of an engine than a specific campaign.
Overall, if you're interested in an small game that *really* integrates PC relationships into its mechanics, I would strongly recommend picking up Bonds. Its engine is extremely robust, almost like a universal Honey Heist, and I have a suspicion that stuff it wasn't designed to run (like survival horror) would work *really* well on it.