Dana Scott graduated Harvard Law School as the top of her class during the year that Harvey graduated as the 5th (though he was supposedly jerking off according to Jessica Pearson). Dana and Harvey have an interesting relationship - while they are rivals in the court, they are intimate outside, and through their experiences in Harvard Law have become very close friends. Dana was recently a Senior Partner at Pearson Specter and was also in a relationship with Harvey.
Harvey and Dana met in Harvard Law School where their relationship supposedly began. In the episode "Play the Man", she tells Harvey that she is going to be engaged when she returns to London.
In her return in "Normandy", she and Harvey agree to work together and she reveals that she never married. She later admits to Donna that she is in love with Harvey and even gives Mike some files to help Harvey win the case against her boss. This causes her to get fired.
Harvey, meanwhile, is still reluctant to trust her saying that she always doesn't give the whole story. He also resents her for cheating on her fiancé with him, as it makes him similar to the men his mother dishonored his father with.
After Harvey loses the case and the merger goes through, he welcomes Edward Darby and asks him to give Dana her job back. Darby then asks him if he prefers that Dana work in New York or in London. Harvey tells Darby that he would prefer her to work in London.
Ava Hessington then sues Harvey and Travis Tanner goes after her and Harvey personally. After Harvey convinced Ava to drop the case against him, she celebrates with Harvey at his apartment. After much bickering Dana noted that Harvey had only told her that he cared about her, in which case he finally admits that he wants more, and they presumably start a proper relationship.
At the start of Season 3 winter season, we see Dana living with Harvey and making Senior Partner at Pearson Specter. As the season progreses, Dana and Harvey fight increasingly, mostly about Mike's secret, which Harvey still won't tell Dana. Donna ensures Harvey that Dana will always find a reason to be angry with Harvey.
In the season 3 finale, Dana finds her arrangement with Harvey to be no longer satisfactory and, after accusing Jessica of becoming Darby, she decides to quit, saying "the only thing holding me back is the non-compete". Jessica discusses it with Harvey who says that if she wants to go, then they should let her.
Despite finding out that it was Harvey who was always covering up his tracks and not Jessica, Dana decides to leave. Harvey also tells Dana he loves her, as well as that Mike Ross never went to Harvard and that he hired him anyway.
Some time after their split, Robert Zane was in a conflict with the firm Dana now works for. Knowing his firm cannot win, he has Harvey use Dana to get them to settle. Harvey tells her that if she doesn't settle, Zane will start digging into his past and find out about Mike's secret. She agrees to this last favor, saying she will never do anything like this for him again, and doesn't want to ever hear Mike Ross's name again.
As she leaves, she tells Harvey that she had loved him, and it is evident that Harvey choosing keeping Mike's secret over their relationship hurt her greatly.