Santana's relationships are hard to keep track of, as she's mainly seen as a 'slut' who really only has sex for the pleasure. She is often assosciated with break ups and has been in a relationship with Noah Puckerman, Sam Evans and Finn Hudson, for various different reasons, all deriving from sexual pleasure and/or breaking them up with an old girlfriend.
The interesting twist to Santana is that there is one person she is deeply in love with, whether she wants to admit it or not - Brittany Pierce. The two often display emotional care for each other, but never have they released this publicly. Santana once tries to reach out to Brittany to tell her her true feelings, but is rejected because Brittany was in a relationship with Artie Abrams; she doesn't bring the conversation back up. During Season Three, however, Santana and Brittany's relationship goes public and the two admit their lesbian orientation happily to one another. Their relationship continues in mutual affection until The Break-Up, when Santana's distance from Lima, Ohio creates tension between the two and they mutually agree to give each other space. Brittany becomes the first to move on when she obtains feelings for Sam Evans. Santana is initially jealous but learns to succumb her feelings to also move on.