As shown in "See One. Do One. Teach One", both Jane Rizzoli and Dr. Maura Isles are interested in Gabriel Dean. Although in the beginning, it seems like Agent Dean is interested in Maura, he begins to pay more attention to Jane and later even offers to stay with her for a night.
In "Burning Down the House", Dean is back in Boston after he asks to be reassigned from Afghanistan to D.C. He visits Jane and tries to start up a relationship with her again, despite Jane telling him about "someone else". They sleep together one night and, in the morning, Jane tells 'Gabriel' about Paddy Doyle after she has him promise to not go after him like the FBI Agent he is. He agrees that he won't go after him until Jane tells him that he can. Later, however, Dean is at the warehouse right behind Jane's team and shoots Doyle after he kills the firefighter that was about to kill Maura, and is later also shot in the leg by Doyle.
In the season premiere "What Doesn't Kill You", Dean has recovered from his gunshot. Jane is furious because she had just found out during her interrogation that Dean had told Internal Affairs about their relationship, and calls him out for following them to the warehouse for Paddy, despite his promise to keep out of it. He later comes by her house, offering flowers, and tells her that he does not believe she is the dirty cop and that she is being framed. He also tells her that he had been called back to Washington.
He has not been seen since.