Vampire Academy

Dimitri sneaking Rose out to see Lissa when she's getting bullied, and Lissa immediately promising to take care of everything.
Even though Rose and Lissa are going through a rough patch, Rose still stands up to Mia and even punches her in the face when she sees Mia yelling at Lissa during the school dance.

"Swallowing, I asked again, “Do you think I‟m pretty?”

He regarded me with utter seriousness, like he always did. “I think you‟re beautiful.”

“Beautiful?”

“You are so beautiful, it hurts me sometimes.”"

Dimitri's concern for Rose after she is attacked by Natalie at the end of the book.
Dimitri's motivation for not wanting to risk a relationship with Rose: he thinks it would compromise Lissa's safety. Even though he loves Rose, he's willing to put his charge's safety and wellbeing above his own happiness.
Throughout the book Rose and Lissa keep Lissa's strange abilities a secret because they're afraid the Academy staff will take Lissa away like they did Ms Karp. They couldn't be more wrong—once the school finally finds out about Lissa they don't even consider taking her away and give her the help she needs to deal with her depression and mental instability.

Frostbite

Lissa's concern for Mia after hearing about the death of Mia's mother. Even though Mia had tried to make her life miserable at St. Vlad's Lissa still feels compassion and empathy for Mia.
Rose's mother comforting her after Mason's death.
After being immature and antagonistic toward Tasha for the majority of the book after learning about Tasha's romantic offer to Dimitri, Rose selflessly tells him that he should take up Tasha's offer because she believes it would make him happy. Then there's Dimitri's
Dimitri

Shadow Kiss

Mia being genuinely pleased to see Rose, Lissa, Christian and Eddie again, after hating and antagonizing them for almost two books.
Dimitri snapping Rose out of spirit-induced darkness.
Dimitri and Rose making love in the cabin, right after Dimitri snaps Rose out of her darkness-induced attack.
After the Strigoi battle, Dimitri and Rose talking about their future now that they've decided to pursue an official relationship together. It's sweet to see them so hopeful about finally being together. Becomes a tearjerker after Dimitri falls during the rescue mission and is revealed to have been turned.

Blood Promise

This line near the end, when Lissa and Rose reunite:
"The door opened, and it was like an apparition materializing before me, some sort of heavenly messenger descended from above. I'd never been away from her for this long, and after all this time, part of me wondered if I was imagining this.
He hand went to her mouth, and she stared at me wide-eyed. I think she felt the same way - and she hadn't even had warning of my visit. She'd just been told I was coming "soon." No doubt I seemed like a phantom to her, too."
Rose's thoughts when she reunites with her mother:
"I loved Olena Belikova. I thought she was kind and wonderful and would cherish the memories of her comforting me about Dimitri and always going out of her way to feed me. In another life, she could have been my mother-in-law. In this one, I would always regard her as a kind of foster mother.
But she wasn’t my real mother. Janine Hathaway was. And standing there with her, I was happy-so, so happy-that I was her daughter. She wasn’t perfect, but no one was, as I was learning. She was, however, good and brave and fierce and compassionate and I think she understood me more than I realized sometimes. If I could be half the woman she was, my life would be well spent."
After everything that happened to her in Russia, seeing Lissa again immediately convinces Rose that she can go on with her life.

Spirit Bound

Despite all of his trauma, Dimitri does not hesitate to help Rose when he thinks she's in trouble, even though it will only cause him trouble.
- Similarly, Rose has no idea what's going on or why the royal guardians are trying to arrest her, but she immediately stops fighting and convinces Dimitri to stand down when she realises that it'll only land him in trouble. Even when they're both convinced there can't be anything between them anymore, they will put themselves into serious danger to keep each other safe.

Last Sacrifice

After the fight with Donovan, Dimitri breaking down in Rose's arms. Rose holds him and comforts him by telling him that she will always be there for him. To snap him out of his self-torment, Rose reminds him about finding the beauty in life and tells him to name anything he sees that he thinks is beautiful. To Rose's surprise, Dimitri says (with an adorable awestruck look in his eyes) that her hair is beautiful.
- Rose's narration stating that she wanted Dimitri to leave the alley one step closer to being the man she knew he could be, and that she wanted him to have one less nightmare.
Sonya and Mikhail finally being reunited.
Adrian reassuring Jill right before the confrontation in the Moroi Court.

Heartwarming / Vampire Academy