She makes him keep the splintmail.

Despite the fact that it took them weeks to find better armour, and that every extra pound of weight was noticeable when they moved camp, she made him keep the full set. He asked why, once, but forgot whatever half-thought answer she gave was, and never bothered to ask again. It lies at the bottom of one of the packs, mostly, never taken out apart from that one time the camp was overrun by darkspawn and he had mistakenly grabbed the old armour in his sleepy haze. She had had such a look in her eyes that night, corpses littered around her, and that steel gaze that was transfixed on him, right up to the point where he had asked her if she was okay - and then it was over, she broke down in his arms and he had held her tight, as if letting go would cause the end of the world.. in his splintmail armour.

He is unpacking his washing, seeing as they are camped by a stream and Wynne keeps glaring at him in that way that she does – the sock incident clearly never to be forgotten – when he finds it again. It is spattered with darkspawn blood and there are a few of her stray hairs stuck in it, but he smiles anyway and places it beside his current gear to be cleaned. After washing comes polishing, and he will have a chance to ask again what was so special about this bruised and battered armour.

She is already by the campfire when he returns, humming a song that no doubt Leliana was singing earlier. He dumps his kit next to her, grinning as she notices what is on top of the pile. She says nothing, however, the only thing giving her away being a slight blush crawling across her face.
"I always meant to ask," he starts. "Why?"
"Why what?" She looks up at him from underneath her eyelashes, and he half-expects her to start fluttering them.
"You told me to keep the splintmail. Why?"
"No real reason."
"Uh-huh. Sure. Because I'm that gullible." He sits next to her, grinning. "It's not enchanted, it's not particularly well-built, it's not special in any way."
"I guess not."
"But you asked me – told me, in fact – to keep it."
"Mhmm."
"So?" She smiles slightly, staring into the fire.
"So. It's the first thing I ever saw you wearing." He is surprised by this response, but says nothing. "It felt.. it felt like some kind of uniform. You were a Grey Warden, and I was going to be one, and I just thought.. I thought it fitted you. It made sense. It worked." She lets out a breath and chuckles. "For the longest time I was looking for some just so I could fit in."
"But Duncan didn't wear splintmail."
"But he wasn't you." She looks up at him. "And let's face it, you look good in it." He laughs.
"It's just splintmail."
"It was never just splintmail on you. Never." She blushes furiously, continuing. "If safety wasn't a problem, you'd wear it all the time, I swear.." He grins, blushing to match her.
"Are you suggesting that you'd rather I wore splintmail than pranced about in no clothes at all?" he suggests, wiggling his eyebrows. She hides her now-red face behind her hands, giggling. "I thought not." He pulls her hands down, looking into her eyes. "But it's a lovely sentiment. When this is all over, I'll never wear anything else, if you want me to." She smiles, kissing his nose.
"Thank you. But maybe it's time to let go." Sighing, she looks down fondly at the armour. "I doubt things are going to get any safer any time soon."

But he keeps it anyway.