Raven and Finn shared a childhood friendship that eventually became a romantic relationship. At some point, Finn made an illegal spacewalk. Finn was caught and placed in juvenile lockup. While Finn was in lockup, Raven stayed faithful to him, even though his future was uncertain. Raven was shown to still love him and visited him in lockup when she could. However, we later learned that it was actually Raven who took the spacewalk and Finn covered for her so she wouldn't get floated.
Raven learned that 100 kids were sent to the ground to see if Earth was survivable. When given the opportunity, Raven bargained with Abby Griffin for a ride down to Earth to be with Finn.
Their relationship became damaged after Finn slept with Clarke, believing that Raven had died in Murphy's Law. Raven broke up with him later on because he didn't love her "the way she wants to be loved" in I Am Become Death.
Raven tried to protect Finn from the Grounders in Spacewalker. She told him, in her last conversation with him, that they "will always be family" and Finn agreed. She was deeply hurt and saddened by his death.
Raven and Finn Collins' grew up living next to one another on Mecha Station. Raven's mother was AWOL most of her life. Raven’s mother often traded Raven's rations for moonshine. When Finn learned of this he began to share his rations with her, saving Raven’s life. In addition, he remembered her birthdays. Raven described him as being "her only family".
At some point while on the Ark, Raven and Finn's friendship turned romantic.
In Twilight's Last Gleaming, Clarke and Finn see the escape pod and think it's a shooting star, but later realize what it really is. They then go and see what it is and find Raven. When they find her, however, Raven kisses Finn. Clarke is in shock that Raven and Finn were actually in a relationship the entire time, when on The Ark.
In His Sister's Keeper, before Finn leaves on the mission to find Bellamy's sister Octavia, Raven kisses Finn goodbye. Raven is staying behind with Clarke so they can look for a transmitter for the radio so they can attempt to make contact with the Ark. Clarke takes her to Finn's bunker where Raven discovers the two-headed deer pendant Finn made for Clarke. Furious and devastated, Raven confronts Clarke about Finn's infidelity.
In Contents Under Pressure, Raven desperately tries to save Finn from his injury, with the help of Clarke. Clarke and Raven encounter many obstacles but are ultimately able to save Finn, bringing the two joy.
In Day Trip, Clarke tells Raven to make sure Finn gets rest while she went out to find the bunker Kane and Jaha had told her about. Later, when Raven is getting water for Finn, Octavia approaches and tells her that it must suck for her that Finn is into Clarke but Raven brushes her off. Raven enters Finn's tent and gives him the water, some spills on him and she begins kissing his neck. She begins kissing him and Finn tells her that something else happened in reference to him and Clarke. Raven admits that she already knows but she doesn't want to talk about it, ever. She continues kissing Finn and the two have sex. At the end of the episode, Finn confronts Clarke about bringing guns into the camp and trusting Bellamy and says he just wished she'd talked to him first, Clarke retorts she wished he'd talked to her about a lot of things in reference to Raven as Raven enters the tent.
In I Am Become Death, Raven, Finn, Clarke, and Bellamy go to the crash site of the Exodus ship in order to try and find out why the ship may have crashed. She later watches Finn run to catch a sick Clarke with no hesitations and feels jealous. Later, while Raven, Bellamy, Jasper, and Harper are making bullets for the grounder attack, Finn enters the tent and suggests building a bomb which Raven promptly agrees to. Finn with a moment of hesitation offers to go plant the bomb but when he goes to find Raven, Monty informs him Raven had already left. Finn and Jasper go after Raven and Finn runs to Raven's aid as she is overcome by the sickness and he carries her back to camp. While resting in the dropship, Raven breaks up with Finn and despite him telling her he loves her Raven says that it is not the way she wants to be loved, and not the way that he loves Clarke.
In The Calm, Finn first finds Raven making bullets and tells her he can tell she's upset but she dismisses him. Later, Raven sleeps with Bellamy in order to try and feel better about her break up with Finn. However, when he asks her if she feels better afterward she says no.
In We Are Grounders (Part 2), Finn is desperate to save Raven who was shot by Murphy. As Raven's condition deteriorates, Finn insists on getting coagulant from Lincoln to slow the bleeding. Raven begs him not to as she fears for his life but he goes anyway. When he returns, he gives Raven coagulant and her condition is seen to somewhat improve.
In Inclement Weather, Raven and Finn have finally reunited, but Raven still has to recover from her injuries. During Raven's surgery, Finn comforts Raven as Abby and Jackson must perform the surgery while she is awake.
In Spacewalker, flashbacks reveal Finn and Ravens past life on The Ark. While Raven tries to study for her test, Finn gives her a birthday present to start a Spacewalk. However after the Spacewalk ends, an alarm goes off and Finn puts on his the space suit to prevent Raven from being executed.
In present time, Raven and the others desperately try to find ways to save Finn from his death. When at the dropship, Raven attempts to give away John Murphyto the grounders in order to save Finn, however, Finn eventually gives himself over to the grounders, to save his friends and the Sky People.
When Finn is about to be executed, Raven gives Clarke a knife to kill the grounder commander. However Clarke knowing there is no other way, mercy kills Finn, bringing Raven to tears and have a breakdown.
In Terms and Conditions, when Raven is helping Jasper steal a chip manufacturer to create more Keys to the City of Light, Jasper's words prompt Raven to realise that not only has she forgotten the pain of Finn's death, she has lost all memory of everything that Finn ever did for her. This realization prompts her to leave the manufacturer where it is, disturbed at the thought of what she has lost.
Raven (shows Clarke her pendant): "He made one for me, too. Just in case you thought you were special."
Clarke: "Do you think I wanted this? I didn't even know you existed. Look, as far as he knew, you were dead, Raven. Or you would have been soon enough. My mom, too, and everyone we ever knew on The Ark, and there was nothing we could do to stop it."