Thráin didn't know when it had started and it certainly did NOT mean he loved his wife less. She was his one and no one could replace that.
He supposed if asked he would have described it as fascination. His father, Thrór, has described it as obsession, but he could go shove it up his arse as far as Thráin was concerned.
He'd first noticed Dori when he was on Erebor watch duty, with his elaborate braids, strong stout stature and firm countenance Dori was the epitome of Dwarfliness and one of the most attractive Dwarves that Thráin had ever seen.
In his flustered state Thráin had blinked many times and ended up in a different place through the pool. He left the pool to give his wife his report and tried to ignore the intrigue he felt over this Mithril-haired Dwarf.
He had managed to put any allure he felt towards Dori aside, yet when he went back to watch over Erebor he found himself unintentionally paying more attention to the stern guild master than to Dáin.
Over the next few weeks Thráin surreptitiously watched Dori when he was supposed to be paying attention to the goings on around Erebor. The captivation he felt with the Dwarf was not as much attraction as it was a deep sense of respect for the Dwarrow who had lost both brothers and carried on.
It was when he was in the middle of one of his watching sessions that Frís appeared beside him. He didn't notice until she called his name gently and asked what he was doing.
Thráin turned towards the person who had just arrived beside him in Gimlin-Zaram and jumped backwards in surprise.
His foot caught in the folds of his long coat and he fell back, his arms pin wheeling and an abject look of horror plastered on his face. Frís stared at her husband in amusement as he looked back up at her sheepishly from the floor where he was still lying prone.
"Frís! Err… hello."
"Thráin. Why are you so surprised?"
"No reason âzyungel. Just watching over Erebor for our inûdoy."
Frís raised an eyebrow at her husband as he picked himself up from the floor, surreptitiously trying to rub his rapidly bruising arse to relieve some of the pain. He couldn't hide the light pink spreading over his cheeks.
"It's Dori isn't it?"
"What? Huh? I… Frís I'm not sure what you're talking about."
Frís left the pool in a shimmer of light and smirked to herself as she heard and saw Thráin scrambling to follow her, "Yes husband?"
"Frís I… I wasn't…"
Frís patted Thráin's cheek lightly, and then stopped him in the middle of the hallway and turned his face towards hers, "I know âzyung. Have you seen the way that everyone looks at him?"
Thráin frowned down at his wife, "I'm not attracted to him ghivasha." She smiled up at him in return, and wrapped him into a hug.
"Thráin, I've been watching him too."
"What?"
Frís rolled her eyes at her husband and supposed it must be his Durin genes making him act like Thorin or Frerin at their stupidest.
"Thráin, seriously, I'm your one, I know you're not looking at others. Dori is beautiful; you are allowed to admire that."
So the next week when Thráin found himself staring at Dori again he didn't feel so bad even when his 'Adad raised an amused eyebrow at him behind Thorin's back and mouthed 'obsessed' at him.