Disclaimer: I own nothing but the plot. Please don't sue me I'm poor.
Two months after the first incident with Ragnar and Lagertha kissing him he was positive that they were doing it on purpose. The kisses, the small touches and the way he would often catch them staring at him. It made him uncomfortable and yet he was curious as to why they were doing this. Were they teasing him? Toying with him? Making fun of him? He was their friend so he was positive they weren't doing it for fun. One day curiosity got the better of him and he just had to ask.
Athelstan had invited Ragnar and Lagertha over to his home to talk. He sat them down on his sofa and steeled his nerves when he asked them why they were doing what they were doing. When Ragnar and Lagertha smiled at him like cheshire cats he felt himself flinch. The two of them grabbed his arms and pulled him onto the sofa with them. He was held by the both of them as they explained.
"We do these things because we like you" Lagertha said.
"We are flirting" Ragnar added.
"But you two are married" Athelstan pointed out.
"That's a good thing. You know we're not trying to cheat and the other" Ragnar chuckled.
"But-but that's not right" Athelstan protested.
"It's fine if everyone agrees" Lagertha said.
"We want you to join us Athelstan" Ragnar whispered into Athelstan's ear.
Ragnar's warm breath made Athelstan shudder and sent a pool of in heat to his crotch.
"Did you like that?" Ragnar asked.
The only response Athelstan could give was a whimper.
It was Lagertha's turn next. She kisses Athelstan's neck and felt him swallow hard.
"Y-You two..." Athelstan stuttered "I-I like you both" he confessed.
After much kissing and caressing the three of them ending up going to Athelstan's bed. Because it was Athelstan's first time they started at a slow leisurely pace.
Athelstan felt himself melting and being moulded by their hands, tongues and touches. The pleasure, the pain, the heat and the passion was exactly as he had always dreamed it would be.
The next morning didn't feel as awkward as Athelstan thought it would have been, he felt happy and comfortable. Days passed and the three of them saw each other more often. After a few months Athelstan moved in with them. After a year a paparazzi leaked a story about them being in a three way relationship, none of them confirmed or denied this and it was fun to tease their fans about it. In fact such exposure made them even more popular and improved their careers further.
And this ends the story of how the mild and geeky librarian Athelstan became a popular model and found friends, family and lovers.