The sunk cost effect occurs when a prior investment in one option leads to a continuous investment in that option, despite not being the best decision. The aim of the present paper was to study the role of the sunk cost effect in committed relationships. In Experiment 1, participants (N = 902) were presented with an unhappy relationship scenario in which they needed to make a choice: to stay or end the relationship. Results showed that the likelihood of participants staying in the relationship was higher when money and effort, but not time, had been previously invested in that relationship. In Experiment 2, the time investment was manipulated and the sunk cost was evaluated using a different methodology. Specifically, instead of having a dichotomous decision, participants (N = 275) choose how much time they would be willing to invest in the relationship. Results revealed a sunk time effect, that is, participants were willing to invest more time in a relationship in which more time had already been invested.