When the series first started, Dustpaw was obviously in love with Sandpaw. He was envious of Firepaw though, when she chose him instead. Around that time Dustpelt noticed Fernpaw, and developed a friendship with her that quickly became mate-status when Fernpaw became a warrior.
Ferncloud and Dustpelt have many litters of kits through the entire series, but both cats face tough timess in The New Prophecy when two kits of Ferncloud's litter of three die. Though arguably not too popular with fans, Dustpelt and Ferncloud are obviously very devoted to each-other.
Rising Storm, page 124
Fireheart wondered grimly what the brown warrior wanted to share with [Fernpaw]. Was Dustpelt poisoning her mind with malicious gossip? But Dustpelt's fur lay smoothly on his broad shoulders, and Fireheart detected none of the usual arrogance in his tone, even though eh couldn't hear what he was saying. In fact the warrior was talking to Fernpaw in a voice as soft as a wood pigeon.
This is one of the first real hints that Dustpelt is creating a friendship with Ferncloud. What's unusual is that this quote is mentioned nearly right after Dustpelt is showing signs of being envious of Fireheart sharing time with Sandstorm. This quote is really a sign of how different his relationship with Sandstorm was then his with Ferncloud. He's soft and protective only with her - as we see later.
Rising Storm, page 124
"Don't worry," Dustpelt assured [Fireheart]. His eyes were filled with uncharacteristic concern. "I'll make sure Fernpaw's safe."
Can we hear an "Awww!" from the studio audience? Yep, this couple is charming in all it's cuteness. This is one of the first times we see Fernpaw responding to Dustpelt. She's so innocent, it would appear as if their relationship started with just friendship on Fernpaw's side.
A Dangerous Path, page 154
"What about the apprentices?" Darkstripe asked. "Do you want them go come with us? Fernpaw's too young to get involved."
"I agree." Dustpelt mewed swiftly.
For all his tension Fireheart had to suppress a purr of amusement to hear Dustpelt betraying the soft spot her felt for Darkstripe's apprentice.
This quote easily speaks for itself. Though Dustpelt, being the defensive cat he is, tries his best to hide his affection for Fernpaw and play the tough tom, it's no secret to the rest of the Clan the way he looks out for Fernpaw's concerns.
A Dangerous Path, page 212
The second question was answered as Dustpelt bent his head and gave her ear a couple of licks. Fireheart had never seen the prickly young warrior so gentle.
"It's okay," Dustpelt mewed. "There's nothing to be scared of. Fireheart won't be angry with you." The glare he gave Fireheart, unseen by Fernpaw, said, He'd better not!
Again, Dustpelt is gentle and concerned with Fernpaw the way he never had been with any other cat, and he is still very defensive of her, letting some of his hostility towards Fireheart show through. Is this his way of saying, "You owe me for taking Sandstorm"?
A Dangerous Path, page 213
". . . Only I've been feeling worse and worse, and so when I saw Dustpelt, I went to tell him." She gave the brown tabby warrior a grateful glance, and he pressed his muzzle against her speckled gray flank.
One of the first times we see Fernpaw's side of her friendship with Dustpelt (which can only be considered a friendship, as she was an apprentice at the time). She really trusts him (little wonder, seeing how kind he was to her). So sweet! :3
The Darkest Hour, page 100
"So, who's going to mentor Fernpaw then?" Dustpelt asked Firestar, taking it for granted that Darkstripe was guilty. "I could manage her as well as Ashpaw," he suggested hopefully.
"Not a chance, Dustpelt. You wouldn't be nearly tough enough with her."
Fireheart's right! If the last quotes proved anything it was that Dustpelt is soft and protective when it comes to Fernpaw, but it's still cute how he hopefully suggests he could take on two apprentices. I'd hate to see Ashpaw neglected in that little mentoring triangle!
Midnight, page 12
Firestar watched, amused, as their father, Dustpelt, padded over to [Spiderkit and Shrewkit], said something sternly to them, then went to sit by Ferncloud.
Ferncloud had her first little of two in between The Darkest Hour and Midnight. We see Shrewpaw and Spiderpaw as mischievous (but oh so cute!) kits in Firestar's Quest. But this also brings up the failing of this ship among fans - we don't even see Fernpaw's warrior ceremony before she's right in the nursery bearing Dustpelt's kits. And she goes in and out of the nursery for the rest of the series - probably spending more time in then out. Dustpelt drastically changes her personality from a quiet, cute apprentice to an uptight, borderline hysterical queen.
Midnight, page 12
Her green eyes glowed as she gazed at the three tiny kits curled up snugly in the curve of her body: one was pale gray like her, the other two brown tabbies like their father, Dustpelt.
*see above point. In MIDNIGHT Ferncloud has had another little; three kits: Larchkit, Hollykit and Birchkit. Unfortunately, only one will survive THE NEW PROPHECY, putting another obstacle in the relationship of Ferncloud and Dustpelt.
Dawn, page 126
"Hollykit is dead!" Ferncloud whispered. "Dustpelt's gone to bury her." She tucked her remaining kit close to her belly. "I woke up and she was cold. So cold!" Her voice cracked with grief. "I licked her and licked her but she would not wake up."
The starvation period is really a tragic one for this couple - Ferncloud and Dustpelt have already lost Larchkit at the beginning of Dawn, and now Hollykit has also died. Shrewpaw will be next - killed by a twoleg monster.
Sunset, page 17
Mousefur bristled at Squirrelflight, but before she could reply she was interrupted by a cry from Ferncloud, racing through the broken thorns that were strewn across the entrance to the hollow. "Dustpelt, where are you?"
Brambleclaw bounded over to her as she stopped just inside the entrance, gazing around the dark and yowling her mate's name.
"I should have stayed with him!" Ferncloud wailed. "I never should have left the camp!"
This part of the book really did make my heart clench. Even if they aren't my favorite couple, Dustpelt and Ferncloud have lost a lot, and the thought of Dustpelt dying (especially when Ferncloud relies on him so much) is pretty heart-breaking.
Midnight, page 18
At the sound of his mate's voice Dustpelt opened his eyes and started to struggle to his paws. Ferncloud bounded up to him, brushing her pelt against his and covering him with licks. Dustpelt let out a steady purr.
Luckily, they are reunited. And they will continue to watch over their single surviving kit - Birchpaw - as he becomes a warrior. In THE POWER OF THREE they will have another litter of kits as well, promising that Ferncloud and Dustpelt have surivived the losses of THE NEW PROPHECY and will continue to be a happy couple.