|“||Listen Moose, you're hot. Yes. My type? Definitely. But you've got more demons than The Exorcist. We're all on the spectrum, but my gay-o-meter says you should stick with what you know best... Girls.||”|
|— Kevin to Moose regarding their fling[src]|
The relationship between Kevin Keller and Moose Mason began as a secret hook up between the two of them after the back-to-school Semi-formal. Slowly, Kevin and Moose developed a romantic relationship, but it ended shortly with Moose leaving Riverdale.
Despite growing up in the same town, it is currently unclear how familiar Kevin and Moose were prior to the start of the series. However, they were at least aware of one another's presence.
Kevin approached Betty at the dance and informed her that Moose Mason propositioned him in the bathroom, and later, he was seen staring at Moose as he was standing with Reggie, but he was quickly pulled away by Betty. Kevin and Moose headed to Sweetwater River after the dance and prepared to skinny dip. The two continued to flirt with one another. As Kevin teased Moose over his secrecy, Kevin tripped and saw Jason Blossom's body, discovering that he had been shot in the head. 
As Kevin and Betty walked the halls of Riverdale High School, she asked him if he was okay after being the one to find Jason's body. He replied that it was even more awkward having to explain to his father why he was with Moose during that time. During biology class, Moose insisted that he partner up with Kevin as the two had to talk about something. Kevin told Moose that he should stick with what he knew best - women. At lunch, Kevin talked about Moose with Betty and Veronica, commenting that he wasn't romantically interested in Moose because he already had a girlfriend, Midge Klump.
Deadly Days at Lovers' Lane
In the late hours of the night, Kevin passed over a bridge as he went deeper into Fox Forest. There, he met a young man of his liking. They were up against a tree, kissing and groping when several gunshots echoed throughout the forest. And while his male companion took off immediately, Kevin decided it would be best further investigate. He made his way through the woods, arriving at Lover's Lane to find Midge, climbing out the passenger's side of Moose's car, screaming for help as she ran into Kevin's arms. Kevin would then learn that they were attacked a man wearing a black hood. Fortunately, Midge was unharmed due to Moose's heroic actions in using his own body to shield her from the gunfire.
The next day, Kevin visited Moose in the hospital. As both Archie and Betty had before him, Moose questioned what Kevin was doing in the woods, though Kevin didn't respond to the question, instead, turning the question back on Moose, asking what he was doing at Lover's Lane with Midge, other than drugs, which everyone had already been made aware of. Moose claimed that the Jingle Jangle was Midge's idea. While Moose liked Midge, he wasn't always sure that they were the greatest match. He then looks to Kevin, who had a troubled look on his face. Kevin told Moose that he hadn't been making great decisions lately. He'd been lying to his father and going into the woods despite knowing the dangers he faced in doing so, almost as if he didn't even care. Moose explained that guys like them, in a town like Riverdale, didn't have many options. So, even if they risk certain danger in doing what they do, they go for it because of the slightest chance that they won't be alone for the smallest amount of time. Growing uncomfortable with the discussion, Kevin decided to leave. As he did so, Moose told him that he could come back whenever he felt like hanging out or talking.
Kevin approached Moose at his locker to see if he wanted to accompany him to the Bijou for the 2018 American romantic comedy-drama film Love, Simon. It was a coming of age film that Kevin was looking forward to, as was Moose. Unfortunately, he had already planned to go with Midge though he did invite Kevin to tag along, claiming that Midge was open-minded and knew all about them. Supposedly, she was cool with it, but Kevin passed on the offer nonetheless as it was a little to Big Love for him.
The following night, Moose and Midge approached Kevin while he was eating alone at Pop's. Midge invited him to join her and Moose in their booth. She assumed that Kevin would be meeting someone at the Bijou, but sadly, he wasn't. Which Midge thought to be unacceptable. She offered to help him find a date, suggesting one of the new Serpents that had recently transferred to Riverdale High following the closing of Southside High. She had heard that at least one of them was gay, Fangs Fogarty. However, Kevin explained that he didn't think he could date someone named "Fangs". Moose interjected that Kevin should at least give Fangs a chance since he was attractive though Midge disregarded his comment. She then asked how Kevin and Moose became friends. Though Kevin and Moose came to know one another through pre-planned sexual encounters, Kevin told her that they were Biology partners.
|Editor's Note: While actors Casey Cott, Cody Kearsley and Moses Thiessen do appear in the following scene, they do not portray the characters whom they are credited for i.e. Kevin Keller, Moose Mason and Ben Button. Instead, they portray two young men who eschew from socializing with women to spend time together.|
During movie night at the Sisters of Quiet Mercy, the patients were forced to watch a film about homosexual deviance that outwardly starred Kevin and Moose. These two seemingly all-American boys chose to abstain from going to the diner with their friends to have chocolate phosphates with the girls, and instead headed down to the river, where they undressed and went for a swim without clothes.
Kevin found Moose crying in the bathroom, Kevin approached Moose to ask him why he was crying and Moose revealed that it was because Midge's things were destroyed in the riot. Later, Kevin hugs Moose, showing compassion for him, then Moose kisses Kevin and they begin to make out. 
Relationship, Coming out and Break up
Problems enter their relationship when Marcus Mason, Mason's stern father enrolls in Riverdale High as the RROTC Instructor. Seeing no other option to spend time with Moose, Kevin decides to join the RROTC, much to Moose's dismay.
With the interference of Cheryl in Moose's closeted sexuality, Kevin gives Moose an ultimatum - coming out to everyone including his father or forgetting Kevin forever. The following day, Moose reveals to Kevin that he had come out to his dad and that he would be Kevin's date to Tom and Sierra's wedding. Kevin and Moose plan an amorous night to spend for the very first time. However, their happiness is short-lived when a group of Gargoyles came and abducted the lovers. As Cheryl and Toni saved the boys and unmasked the Gargoyle King and the gang, it shocked Moose as it was revealed to be his father, Marcus, and the other RROTC members. Marcus explained his plan to establish fear in Moose just like the Sisters of Quiet Mercy developed it in him when he was infatuated by a fellow RROTC member, Tom. While betrayed and not safe even after Marcus being arrested, Moose moves to Glendale to live with his aunt, breaking up with Kevin.
With Moose leaving Kevin, the disrupted Evelyn Evernever starts to interact with Kevin and soon form a close bond. Brain-washing Kevin into believing that it will help him move on from Moose, Evelyn makes him the newest member of The Farm, much to Betty’s dismay.
Season 1 Screencaps
Season 2 Screencaps