Title: Galen Tyrol
Content:  Tyrol identifies her as Boomer to Adama who promptly orders her thrown in the brig. Tyrol is reluctant to visit her initially but he is later shown looking at her through the glass pane of her cell as she sleeps. In "Someone to Watch Over Me", he visits her again and Boomer shows him the life they could have had, using Cylon "projection", they had planned for before the war had started, including a 'daughter'. Galen attempts to dissuade Roslin from handing over Boomer to the Cylons for a trial, afraid that they will kill her. However, Roslin refuses his request. 
Title: Cylon (Battlestar Galactica)
Content:  =Sharon "Boomer" Valerii first appears as a Raptor pilot aboard the Galactica. Her true nature as a Cylon was revealed at the end of the miniseries. She acted as a sleeper agent, unaware of her true nature and programmed to carry out attacks on the fleet without realizing what she is doing. She was revealed to be an Eight in the episode "Downloaded".
Title: Number Eight (Battlestar Galactica)
Content:  While Boomer is in the brig, Gaius Baltar manipulates her into revealing how many other Cylons are hidden in the fleet. While Boomer is being transported from the brig, Cally shoots and kills her. In "Downloaded", Boomer's consciousness is downloaded into a new body in Cylon-occupied Caprica. She resists being identified with the Cylon cause despite being viewed as a hero alongside Caprica Six, and both she and Six decide to try to persuade the Cylons to reduce hostility against humans. Later in the series, Boomer appears among the Cylons occupying New Caprica as a member of the Cylon governing council controlling the human puppet government.
Title: Flesh and Bone (Battlestar Galactica)
Content:  Starbuck captured. Having followed Boomer's advice to treat the Raider as an animal rather than a machine, Chief Tyrol and Starbuck have had some luck in deciphering many of its basic controls, but Tyrol is now suspicious that Boomer is a Cylon and remains distant from her. Having heard of Baltar's Cylon detector, Boomer visits him to get tested. After Boomer reminds Baltar that she saved his life on Caprica and that Helo gave up his seat for Baltar, he agrees to use Boomer as a Beta test, learning in the process that Boomer's entire family is dead in a mining accident that destroyed her whole colony. Baltar's Cylon detector reveals that Boomer is indeed 
Title: Kobol's Last Gleaming
Content:  to arrest her. A standoff ensues between Colonel Tigh and Apollo, and Roslin surrenders to avoid bloodshed. Both she and Apollo are sent to Galacticas brig. Adama orders the Boomer on Galactica to destroy the Cylon Basestar orbiting Kobol: a captured Cylon transponder allows Boomer's Raptor to penetrate the Cylon defenses. The launch system jams, so she is forced to land the Raptor inside the basestar and release the nuclear warhead manually. There she encounters several copies of herself, proving to her that she is a Cylon. She flees in the Raptor, destroys the basestar and returns to Galactica. Under the influence of her Cylon programming, Boomer shoots Adama twice in the torso.
Title: Cylon (Battlestar Galactica)
Content:  Cavil and Boomer, whom he'd let in on the secret. After Cavil planned to dissect her brain to try to regain resurrection technology, Boomer helped Ellen escape to the fleet as part of a plan to kidnap Hera so the Cylons could study her. Galactica and some of the rebel Cylons assaulted the Cylon space station that was the Cylon homeworld, to rescue Hera while the Rebel Basestar protected the fleet. During the battle, Boomer, who had begun to feel remorse for kidnapping Hera, killed the Four that was starting to dissect the child and returned her to her 
Title: Number Eight (Battlestar Galactica)
Content:  Lieutenant Junior Grade Sharon "Boomer" Valerii is a Cylon sleeper agent programmed with false memories of being raised in the mining colony Troy by parents Katherine and Abraham Valerii, who supposedly died in an accident that wiped out the colony population. Before the mini-series, Boomer and Galen Tyrol are romantically involved, which is against military protocol due to their ranks. Her programming leads her to black out and sabotage the Galactica on several occasions, which Tyrol unwittingly abets by hiding evidence implicating her. In "Kobol's Last Gleaming", Commander Adama sends Boomer on a mission to destroy the Cylon basestar orbiting Kobol; and after her return, she shoots Adama twice in the chest, putting him in a coma and revealing her nature to the crew.
Title: Downloaded (Battlestar Galactica)
Content:  Inner Six, and Boomer is having problems accepting her Cylon nature to the point of the denial, even in danger of being "boxed", which means storing a Cylon's memories without consciousness out of its body. Number Three (Lucy Lawless) asks Caprica-Six to help Boomer in this regard. However, when Caprica-Six starts to associate more with Boomer, they both realize that the holocaust the Cylons effected was a sin. They also come to the conclusion that due to their unique perspectives, Number Three is searching for a reason to box them both, fearing their acquired humanity a flawed corruption. Caprica-Six and Boomer are next shown conversing with Number Three. While the 
Title: Number Eight (Battlestar Galactica)
Content:  Boomer is the only other Cylon who knows that their creator, Ellen Tigh, is being held prisoner by Cavil. When Cavil threatens to cut open Ellen's brain in order to access her knowledge about Resurrection technology, Boomer helps Ellen escape, but is immediately imprisoned after disembarking on the Galactica. She escapes with the help of Tyrol, who is motivated by sentimentality.
Title: Cylon (Battlestar Galactica)
Content:  pursued them while initiating the next phase of their evolution, procreation. Female human survivors were detained and used in experiments to create Cylon-human hybrids. The experiments were unsuccessful leading the Cylons to conclude that the missing component was love. They tested this by using an Eight posing as Lt. Sharon "Boomer" Valerii from Galactica to seduce a marooned Galactica officer, Lt. Karl "Helo" Agathon on Caprica. They fell in love. The Eight abandoned the Cylons, helping Helo to escape. The couple later produced the first viable human/Cylon birth. This Eight joined the fleet with Helo. She later married Helo, joined the Colonial military and received the call sign "Athena". Ten months after the initial attacks, Eight Sharon Valerii (call sign "Boomer"), attempted to assassinate Commander Adama under the influence of 

Question: when does boomer find out she a cylon?
Answer: Kobol's Last Gleaming.