How people choose to spend money is often observable to others (e.g. based on their clothes, accessories, and social media pages), but there is a whole universe of financial decisions that are essentially unobservable (e.g. how people handle their debts, taxes, and retirement planning). We explore one context where people have an up-close-and-personal view of someone else's financial decision-making process: romantic relationships. We discuss how the endless opportunities for financial observation in romantic relationships influence a range of behaviors, including spending habits, decisions about bank account structure, and financial infidelity. Our review highlights the need for more research on the ways in which financial decisions are made, communicated, and observed within romantic relationships.