Terry ofter rode together with Ronnie and Lem while Vic and Shane were most of the time riding together. It is revealed in "Co-Pilot" that Terry was previously unknown by neither one of the team but he was immediately liked by most of the Barn and Strike Team after being introduced due to his humorious and good-natured personality and for being a effective and competent detective.
While it may appear that Terry was close with all of the team members, the most close with Terry was Curtis Lemansky who immediately took a liking into the young detective and both were seen together most of the time in the Strike Team clubhouse with the rest of the team and telling numerous jokes.
During a raid on a drug dealer's house, Lem and Ronnie followed the drug dealer's girlfriend while Vic, Shane and Terry faced the drug dealer Two-Time. However, Terry was shot in the face during the gunfight and was taken to the hospital. While Terry was operated on, Lem, Vic, Shane, Ronnie etc gathered outside the hospital and waited to find out if Terry lives. Lem shouted: "NO!" and lacerated his right fist after punching a van window in grief upon hearing that Terry died.
There are numerous indications that point that Lemanky greatly cared for Terry and that they were close friends. The first is his reaction to Terry's death, the second is when he attended Terry's funeral and the third is when he is seen to be notably guilty several times as he believed that he and Ronnie failed to clear the room which resulted in the death of Terry.
What Lem did not realize was that Terry was in reality an informant for Aceveda and the Justice Department and that he was killed not by Two-Time, but by Vic. Lem did not know this shocking information until Season 5 when IAD Lieutenant Jon Kavanaugh, who investigated the team about their role in Terry's death, informed him about this and blackmailed him into wearing a wire and gathering intel. After singnaling Vic and removing the wire, Lem tells him about the situation and unexpectedly asks him if he truly killed Terry. Before Vic could answer, Lem told him not to answer as any answer would mean that he killed Terry.
Despite promising that he will betray the team if he found out that Vic killed Terry, Lem, however decided not to either because he could not betray his "family" or because he also agreed that Terry had to die as he would have set them up to be in prison. However, Vendrell, who was wrongly told by Aceveda that Lem was going to testify, did not want another Terry Crowley and killed Lem with a grenade.
After realizing in Season 6 that Vendrell killed Lem, Vic confronted him but he sincerely apologized and attempted to justify his actions by comparing Lem's murder to Terry's murder as a way to protect the team. Vic does not accept this comparison and angrily tells Vendrell that Terry was traitor who had to be put down while Lem was loyal to the team to his last breath and did not deserve a fate, similar to Terry's.
In Season 7 in order to gain immunity, Vic testified infront ICE agents and exposed himself and Vendrell as Terry's and Lem's murderers respectively. After Vic angrily taunted Shane about his immunity deal and crushed the last hope Shane had for freedom with his family, Shane killed his own family and then shot himself in the head, committing suicide. Thus, Vic indirectly avenged Lem's murder and killed the second man who was part of the plot to murder Terry. Since Shane was dead and Vic already made a deal with ICE, Ronnie was arrested for his role in Terry's and Lem's deaths even though he had no role in either of the two fatal plots against his team members and cursed Vic for his betrayal upon being led away.